Define "development"

If White plays 1.Nf3, White has developed a knight.  This much is obvious.

But if White later moves this knight once again -- on move 6, perhaps -- can we say that the knight has been developed again?  Would move 6 qualify as a "developing" move?  Or is it not possible, by definition, to develop a piece twice?

As another example, let's say we're in the endgame.  The same knight is on the rim, and useless.  But White now moves this knight to the centre, making it a strong piece.  Again, can we say here that White has developed the knight?  Or does "development" apply only to the opening?

In other words, my question is as follows:  Does the chess term "development" simply mean "moving a piece away from its starting position, in the opening of a chess game", or does it mean "moving a piece to a 'better' square (even if it's been moved before), in any phase of a chess game"?

Development means you've moved it off it's starting square for the first time.  If you move a knight to c3 and 15 moves later see that you really need it on d2 now and play knight at c3 to b1 and then from b1 to d2 it's not called development anymore, you're just maneuvering it.  You could call it maneuvering, or improving the knight. 

I think I also saw the term "redevelopment" once to describe a series of maneuvers of the pieces to the new optimal squares which is fairly common in a closed position, so you could use this term too.

In the case of a useless piece becoming strong, as in the example you gave of the knight on the rim going to the middle, you'd just call that activating the knight, getting the knight active, bringing the knight into the game, etc.

Development usually refers to the opening, not necessarily to a move that takes a piece off its starting square, but one which puts it in a good place. You might put your knight on the edge and then move it closer to the center. I would call the second a developing move, not the first. Through middle and endgame I guess its just called a good move.

While it's true an annotator might say at move 10 "white has developed his forces well, especially his knights to c2 and f3 to fight for d4," strictly speaking the first move is the only move called development, afterwards it's just maneuvering.  Even though it wouldn't really matter it would be more correct to say white developed his knight to a3 to later move it to c2 where it joins the fight for b4/d4 etc.

I don't see development as a technical term, just as middlegame doesn't really have a technical definition of a beginning or ending. It is a stage, and you can tell when you are in that stage even if you can't point to a reason. In more official settings one might desire more precise definitions, but I just don't feel right saying that white developed his rook to g1 unless he's got a half-open file there.

But if you  move that rook to g1 and then 5 moves later play g4 as part of a kingside attack it makes sense.  So can we only determine if it was really development many moves later when it's proven a useful vs a bad move?  Not really, bad development is still development 

Not that I really disagree with you.  After 15 or so moves I may look at the position and consider how each side had "developed" even if half the moves weren't in the strictest sense developing moves.  Still, if I notice some of the pieces are misplaced I still think of them as being developed there, I'll more likely think his forces are unorganized.  On the other hand if my opponent has a bishop, knight, and rook on c1, b1, and a1 then I try to open up the position/attack because his queen side is undeveloped.

I go by the definition that it moved off its starting square. This doesn't imply that it's automatically a good move moving it off it's starting square, but I think that's usually what people mean when they say development.

Thanks for the replies so far.  This word "development" has always bothered the pedant in me, so it's interesting to see what others think here.  :)

As far as I know, ''development'' means moving your knight away from it's strating point, and if this same knight get into the center of the board, this is not a development anymore, you will call it this now a ''strategic position''.