Difference between inaccuracies, mistakes and blunders.

Could someone please tell me the difference between inaccuracies, mistakes and blunders.

Inaccuracy is none of best moves, somewhat bad.
Mistake is a clearly bad move.
Blunder is a very bad move that might cost you the whole game.
Imo.

Within a given position there are often many legal moves at one's disposal. The available moves vary in terms of quality from best to worst. Almost always there is only one best move... and that one best move can range in quality depending on the position from sterling ' flawless ' to ' not so good ' but the best available considering the options. Sometimes it may come to pass that there may be several 'good moves' available to choose from and ' the best move' may only be slightly better than said ' good moves'.

a blunder is a strict loss of material, position or both.

a mistake tends to be a positional concession, something that can lead to bad things down the road. the computer does not seem to consider the loss of one pawn, without corresponding positional weaknesses, as a mistake.

an inaccuracy will be something along the lines of a move order mistake, an acceptable move was made, but a better move was on the board. the loss of a pawn in the early to middle game may fall in here.

hope this helps

Generally speaking, yes.

But here there are simply 3 intervals for eval(yourmove)-eval(enginemove), sheer mathematics

Other than the above mentioned 'best move' and 'good moves' there are the bad moves... and the bad moves can be divided up into three catagories: inaccuracies, mistakes, and blunders. The blunder is the worst of the worst sort of bad move... the blunder can result in signifigant material loss... if I hang a pawn and that pawn is captured by my opponent it doesn't mean that the game is lost ( depending on the position ) but if the loss of that pawn does result in a lost position than hanging that pawn would be considered a blunder... basically blunders lead to lost positions which means you can't win unless your opponent doesn't execute perfect play... ( must keep in mind that a won position is not always easy to win... but technically speaking if the bad move leads to a lost position than you can consider that bad move to be a blunder.)

I think, in Lichess, if your move is between 0,5 and 1 pawn worse than the Stockfish suggestion is a inaccuracy, if your move is between 1 and 3 pawns worse than the Stockfish suggestion is a mistake and if is above 3 pawns worse is a blunder.

But, that's in an about equal position. In a very much unbalanced position you can lose more pawns and not be considered a mistake.

A mistake is a very bad sort of move that doesn't result in a lost position ... it is possible to hang your queen, lose that queen to capture, and yet, due to possible compensation, your position is not a lost position. If your position is not a lost position than the bad move would be considered a mistake.

Of course there is a more technical definition available of the blunder, mistake, and inaccuracy.... I'm just offering concrete generalizations. Are you asking about this for programming purposes or for a general understanding of the game... in other words: why th e question? as far as inaccuracy goes that's like quantum level chess physics to me...( above my pay grade) I've seen moves that I personally would consider to be an inaccuracy but stockfish sees it to be a good move ( go figure... ha,ha... literally go figure.) well, good luck with your quest to understand such things. hope I was able to contribute in some way.