I consider laggy something which is going slower in relation to something else.
So in computer language and aside from networking and stuttering, it can still be used properly.
For example any game which is pushing the fill rate of the videocard too much will usually slow down keyboard and mouse response, and when having the character move on screen half second after a key was pushed you can safely say: "keyboard response is laggy".
To name one, I noticed with surprise that it always happens in Lost Planet, even on really good hardware and after lowering the detail... the graphics run really fast, but between mouse and screen response there are about 300ms of lag (to me it looks like improper handling of logic cycles for the controls).
So in computer language and aside from networking and stuttering, it can still be used properly.
For example any game which is pushing the fill rate of the videocard too much will usually slow down keyboard and mouse response, and when having the character move on screen half second after a key was pushed you can safely say: "keyboard response is laggy".
To name one, I noticed with surprise that it always happens in Lost Planet, even on really good hardware and after lowering the detail... the graphics run really fast, but between mouse and screen response there are about 300ms of lag (to me it looks like improper handling of logic cycles for the controls).