what is an "inaccuracy"?

Inacurracy = Not the best move, but not a losing move.

Mistake = A move that takes your position from winning to even.

Blunder = A move that loses the game.  

No, FishEyedFool is incorrect, at least as to the terms as used in computer analysis -- he is giving you the evaluation that humans use or trying to -- I'm not sure its 100% accurate.  But I think your asking for the meaning as used by the evaluation of the computer, and as used in computer evaluation, these terms correspond to the difference in the computer's evaluation between your move and the move the computer believes is best.  I believe a blunder changes the evaluation by at least + or - 1, whereas mistake is something less than that, and inaccuracy is even less.  In practical terms, a chess player of your rating should focus most heavily on trying to figure out why the computer is calling something a blunder.  Mistakes and especially inaccuracies will often be inscrutiable (and this is also true for much higher rated players).  

An inaccuracy is something you want to avoid. A mistake is something you really want to avoid. A blunder is something you really, really want to avoid.

Sine the parameters on a chess engine can be changed, it didnt make any sense to address what an engine thought.  And since we play people, i thought it made more sense to define them as to how we as humans see them.  

 Let's say a cop pulls you over. He approaches the car and you roll down your window.

Good move: "Good afternoon officer. What's wrong?"

Inaccuracy: "What did I do?"

Mistake: "God, don't you have anything better to do?"

Blunder: [pulling out your wallet really quickly] HA! Gotcha!

inaccuracy - less than 1 pawn lost mistake - 1 to 3 pawns lost blunder - more than 3 pawns lost in one move

Reminds me of that Chris Rock skit.

 I need to watch more comedy routines--his and many others.

[Abuse removed; DS]

In football (soccer): inaccuracy is passing to the wrong player on your team; mistake is giving the ball away to the other team; blunder is scoring an own goal.

A bit since I laughed out loud all alone. Thanks guys!

Can't stop laughing actually   

Inaccuracy is not very clear when the computer analysis in 1minute. For ex, Bobby Fischer sometimes has moves when it seems that better moves instantly; but 8-10 moves later this move became an "!!" Perfect move. Mistakes changes your clear wins into a little advantage or neutral. But blunders changes mate in .... moves into drawn, or clear wins into loss.

In my opinion, Inaccuracy makes us unsecure up to 10 percent it means if the opponent catches it in time he/she can take advantage of that, resulting in 10 percent of their winning chances and losing chances for us (or losing a piece or two). Mistakes i would say it 25 percent plus definitly lose a piece or expect more damage... while blunder its 50 percent losing chances expect to lose. But winning after a blunder is hard but not impossible, depends on opponent's strategy and tactics and our luck because something the opponent makes even bigger blunder than our's. 

Pawn:can I move like this (the move is inaccuracy)

King:IDK JUST MOVE IF U WANT

Inaccuracies do not exist.
Either a move worsens the game state won / drawn / lost, or it does not.
If it worsens the game state, then it is a mistake (?) instead of an inaccuracy.
If it does not worsen the game state, then it is not inaccurate.

Every reader should be warned that this is tygxc's own definition which no one else uses and no one agrees with. Chess.com uses these terms differently.

Not to mention that the OP probably got his answer in the past 6 years.

I have certainly won games in which I was evaluated as committing one or more blunders (maybe the opponent did worse). More often, alleged mistakes have actually set up a win. At least at lower levels they do not necessarily have the negative effects that might be expected.

Inaccuracy come where you mad a bad move. Not that bad but is something you want to avoid. It leads to a very bad move. However you can fix it. If you made an inaccuracy move, try to fix and adjust that move. Try to make the game better. And inaccuracies do exsist.