In reply to stp:
We have to have umbrella terms for styles of ascent or else headlines would take all day to read! But within each umbrella term is a massive variation of awesomeness....
Onsight: Means a no pre-practice or beta, no falls ascent, but within that style you have a spectrum - turning up at the crag, deciding you will have a crack at that piece of rock in front of you, not knowing if it can even be climbed is the purest. The minute you know a grade, that it can be done, the purity lessens. The other end of the onsight scale would be climbing your route when it has had a raft of previous ascents, been chalked and cleaned, you've aspired to the route for years, dreamed about it, read all the descriptions in several guidebooks, done all the other routes at the crag, you get the picture! It is still also an onsight if you (shock horror) have some gear in situ, the lowest of the low OS ascent. Clearly it is less impressive though.... and you would have to call it an onsight with pre-placed gear.
Flash: First go, with knowledge. But I know people who have taken flash instead of onsight just because someone shouted "left!" as they were mid route on an otherwise knowledge-free ascent. I also know people who have taken the flash after abseil inspection, cleaning holds, looking at the gear placements (but not trying any moves), watching numerous films, building replicas, getting the blow-by-blow account from a regular climbing partner. It's still a flash, but a waaaay inferior one. And yes, you can flash on in situ gear - it's just even more inferior!
Ground-up: Climb from the ground up with no pre-practice. When you fall, you lower straight down to try from the floor again - having a sneaky play on the next moves after a slump invalidates the ground-up.... And within this umbrella term you have a pure onsight attempt (new route, no info or cleaning), getting your mate to retrieve your gear between attempts so you can place it all again - pure ground-up. OR an 'inferior' flash attempt with all the beta, clean and chalked holds, you fall off, pull the ropes and go again on the gear you already placed. And anything in between.
The point is; for all these labels there is an enormous sliding scale of ethics. Some onsights are better than others, some flashes are better than others, some ground-ups are better than others. The important thing is to be honest about how you did it.