Technically that’s a fall. You fell down. But that’s boring, how do we fit it into our nerdly arse-covering terminology for the lack of staying on the uni? In the situation described above, BPD would stand for Botched Planned Dismount. Or a UPD with extra style points, if you like. 
In the real world, I mostly use “fell off” in conversation, for obvious reasons. By that I mean, not wanting to explain what a UPD is, and why we have to make up a TLA for falling off!
In response to the occasional UPD around people, they ask “Are you alright/ok?”
I say that I am fine and at least I landed on my feet!
I sometimes have to explain UPDs to MTB’s and other people who ask how many times I have fallen off.
The quickest response is to say, “Loads of times!”
Exactly! If you’re not falling off then you’re not riding hard enough stuff. Generally if I havn’t fallen it’s because i can only find really boring terrain…
My response to such a question is usually along the lines of “You mean today? Otherwise I can’t count that high.” 
Always fun to revive a zombie thread!
It’s hilarious that my attempt to re-define an ‘oops, I fell off’ situation as a UPD ended up as slang for both falling off AND falling splat. I really wanted to distinguish between the two; in fact, I even made up a six-level rating for UPDs (as a joke) based on the six-level rating for tornados (the Fujita scale). Like the tornado rating, level 6 has never been recorded. A level-six UPD meant death, so I’m glad we still have such a good safety rating!
Anyway, I used to have a unicycle blog and apparently used the term UPD (to mean falling OFF the unicycle but landing on my feet) back in 2001. I’m fine with it being used in an unintended manner – such is the nature of language!
Here’s a link to my blog (I can’t believe it’s still accessible!)
To me it is when something throws me off the uni and I can outrun it. My impression is that for the majority on this forum the bit about outrunning is not part of the definition. If I can‘t outrun it I consider it a fall.
I wasn‘t aware of the acronym UPD until I started lurking on this forum and it made quickly its way to my vocabulary - after all its kind of daily business, either because it happens or because it almost happens. Fortunately the latter is way more common than the former.
It should be used as a verb, as well as a noun, as you can dismount, and you can do a dismount.
What about when you go too fast and get thrown off, landing in a run?
Skateboarding and uni’ing are alike in that you can fall off the vehicle and end up on your feet OR you can end up on your butt. On the other hand, if you fall while skating or skiing, you are never landing on your feet, so those activities don’t need to distinguish between the two.
I’ve noticed that I usually do plannified UPDs (PUPDs) while freewheeling or coasting. I know it doens’t make sense, but I hope you can understand then and possibly note if you also do then with the next explanation.
When I am coasting both on a freewheel uni or in a free uni I can have a UPD when I loose my balance, but I noticed that when I want to get off the unicycle instead of just leaning back and putting my feets off the pedals, I just stop trying to maintain the balance, which results in a UPD and is kinda like a game of “how far will I go?” (I now remember that one time while doing that with the feets on the frame, one feet went in the way of one pedal so I fall backwards, so it may sometimes result in falls too🥲). I think that I started doing this due to my love to coasting, I love to be coasting, but sadly sometimes you gotta stop, so as I would feel bad with myself for ending a good coast on purpose, I started doing it in this way so that, even though I am the one who decided to stop fighting for balance, it feels like it wasn’t my fault.
Then, as for the types of UPD/falls/dismounts, I like to follow the next logic of terms that you can combine:
Your list is similar to the one I jokingly developed based on the hurricane/tornado scale. Basically, level 3 was a fall (where you don’t end up in a standing position), level 4 was a fall where you sustained a small injury and/or some pain, level 5 was a bad fall where you ended up unable to ride (either you or the unicycle was broken in some way), and level six was death (I called it toe-clips because it’s so crazy to ride with toe-clips, tho I know that some people have done it).
Level 1 and 2?, I supose level 1 is just a good dismount, but I’m curious about 2.
1 = you fall off but catch the unicycle (it doesn’t hit the ground)
2 = you fall off, and the uni hits the ground (but you’re still standing)
3 = you and the uni are lying on the ground at some point (or at least, you’re on your knees, etc)
4 = slight injury (scrape, bruise)
5 = you can’t ride away from the UPD (one of you sustains a break)
This happened to my brother once, but I don’t think it ever happened to me. He was riding in the Alps (without a brake) and couldn’t slow down during a steep descent. He fell off and was banged up a bit, but his unicycle was damaged to the point where he couldn’t ride it. (It was an ungeared Coker, if I recall.) A rider on the Lobster was using toe clips and fell off such that he landed on his knee, shattering bones. Poor guy’s wife had to drive them from Nova Scotia back to Alaska (5000 miles); she was pissed!
So if I breake my left wrist (which happened) it would be a 4 or a 5?, I could still ride with almost no problems as I doens’t need my left wrist for unicycling (I break with my right hand), but it isn’t a slight injury either. In my case it was a 5 because I also hit my head so I was dizzy and coudln’t see well, but in the long term, luckly, the wrist was the main problem since I couldn’t carry my luggage well (two unicycles and big backpack) in public transport to return home from the unicycling weekend (1 bus, 2 trains and some subway ), so someone very very very kind drove me home (he lived far from where I did).
We’re going to call that a level 5 because of the moderate head injury; breaking your wrist would make it level 4 since, as you point out, you could still ride safely.
Sounds like a really awful fall! And it makes me wonder how many level 5 falls have happened? We all know of a few (and some of you have experienced one or more). I’d guess that there have been hundreds or even thousands of level 5 falls. Luckily, still no level 6s!
You know when Pee Wee Herman was doing some bicycle tricks in front of the neighborhood kids. He crashed and then he stood up and brushed his pants. Then he said “I meant to do that”.
That’s what unicyclers mean when we UPD.
Right, Pee Wee!!!
…slam
To be honest, in my 9 years of riding I never got to level 5. I always ride very carefully. Naturally I tumble off every once in a while, for any reason, like riding over roots or forgetting I only have one wheel. The only sort of injury I sustained is a painful knee, when I was going all in for learning to ride an Ultimate Wheel. Now I can, but in the process I twisted my knee joint, which still hurts when walking stairs or applying a bit of force when uni-ing.
Oh at what level does a failed dismount fall, like when I plan to have a gracefull backwards dismount in 100 meters, but somehow I dont get the balance right and half jump forwards, the uni falling on the ground or if im lucky trailing behind me coz the seat is still in my hands?
Well, most of us, thankfully, never hit level 5. I’ve never been unable to ride following a UPD, tho I’ve definitely sustained some really nasty scrapes. But I’ve never had a broken bone or a broken unicycle (or even a broken crank as a result of a fall), so my worst has been a few level 4’s.
Quoting my blog piece from 2002 (yes, over 2 decades ago!), which was based off a scale for hurricanes:
S-0 “Light” Rider lands on feet at a walk or jog, rider catches uni, no damages or injuries
S-1 “Moderate” Same as S-0, only rider lands at a run
S-2 “Considerable” Rider lands on feet, often at a run, but unicycle hits the ground
S-3 “Severe” Rider actually falls but is not injured; potential for embarrassment
S-4 “Devastating” Rider falls badly and is scraped up or bruised; rider is able to ride
S-5 “Incredible” Rider’s injury prevents further riding for some time; uni likely damaged
S-6 “Toe Clips” Rider is killed, the result of poor judgment and/or unsafe conditions
I love how you titled the death condition as “Toe Clips”. 
I used to ride without a helmet, gloves, elbow/knee pads… But about a month ago I had a level 4 UPD.
I had gotten back from work and I had wanted to do some more riding on my 36er using 114mm cranks. I was still getting familiar with the uni in general, but at that point I had done a lot of riding on the 142mm cranks. I started riding around with the different crank setup, and I felt like I could push the uni a bit more than I could with the 142s!
Well… I got a little carried away 
I leaned a little too far forward, and just by reflex I started pedaling faster and faster (meanwhile I’m trying to lean back but my legs were like go go go). Soon enough I flew off of the unicycle, I land running way too fast, and I fall into a bad roll. Got some road rash and bruising on my hip and lightly scuffed palms… Could’ve been worse as I did ride away, but after that I decided I’d rather be safe than sorry 