How long is an opening?

How exactly is an opening defined, and how many moves does an opening consist of?

From my own very limited experience as an absolute beginner, It seens as though you have prety much set your stall out with your first 2-3 moves.

Well, the answer is, "Depends on who you ask" and "it depends on the opening."

A good enough explanation from the wikipedia entry on the Middlegame:

The middlegame in chess refers to the portion of the game that happens after the opening and before the endgame. There is no clear line between the opening and middlegame, and between the middlegame and endgame. In modern chess, the moves that make up an opening blend into the middlegame, so there is no sharp divide. At elementary level, both players will usually have completed the development of all or most pieces. The king will usually have been brought to relative safety. However, at master level, the opening analysis may go well into the middlegame.

I'm not sure there's anything exact for that! If you're talking about ''the first classification'' you will see it early. For example we can say 1.e4 e5 2.Nf3 Nc6 3.Bb5 is the Ruy Lopez or the Spanish. However you can go deeper and look at the variation and then the sub variation. Every time there is a defining move in the junction that gives the opening that name, rather than another. You understand 1.e4 e5 2.Nf3 Nc6 3.Bc4 is the Italian, rather than the Ruy Lopez.

The intuition of most people is that the opening is effectively ''over'' when the pieces are developed. (An exception can be Bc8 of course.)

Some lines are very forcing and go on well after that. Then we should say ''the opening is over when there is no more theory or when we are out of book.''

Generally, the opening ends when all of the pieces are developed with the rooks connected, etc.

I consider there is opening when the moves are made by opening ideas or concepts, and the opening is over when the moves are no longer moves that folow the opening ideas.

This ideas are: development, center and safety of the king.

The opening is over when the player gets out of this ideas and make moves that go on the midlegame, like tactic, or even moves that go on the end of the game, as for example upgrade a passed pawn or so.

I consider development the most importan part of the opening. This is bringing the small pices (knigth and bishops basically) out. to squares that are hopefully better than where they where. This have to be done as soon as you can, and avoiding moving the same pice 2 times on the opening, unlest you are in danger of losing or in oportunity of winning.

The center is a very importand area of the board and from the beginig you should try to get as many squares you can, this is the justification on moving pawns, on the opening, to get the center and to open lines to alow bishops to go.

The safety of the king is ironically on the opening no as much of priority than other ideas. For the oponent is not yet developed, so if atemping to atack most likely will end up in nothing. So be aware of crazy opening atacks, but know that 1 single pice can't do mate, so what they are looking for is just some dance, usually between your king and their queen.

So considering to be aware of the strom mates people sometimes atemp on the openings. The concept of safety of the king is more relate to for the midle game, when the oponent have material developed and can coordinate some serius atack.

I personally don't translate castle to safety of the king, so depending on the board you should consider king side castle, queen side castle, or no castle at all. But whaever you chose, make sure the king is safe. Another thing about castle is that you should aboid it early on the game, Usually some 10 moves on the game is a good time to start considering castle. by this  time you ready can see how the oponent developed material, on what side you are stronger (castle on your strongest side) and can consider it better, if you castle too soon, then the oponent will start preparing the atack to the king while developing, not good.

After the moves are no longer made With this concepts behindthem I consider the opening is over.

Also if the first move is something like a3, I would say the player didn't had an opening on his game, for this kind of moves doen't aim for any of the opening ideas.

Except for the fact that is actually a named opening; A00: Anderssen Opening

It has been played in 301 games from the Chess.com game explorer of Master level games. It even gets played by Carlsen in blitz :D

Thank you for all your comments and thoughts and ideas,  I am enjoying learning from you all.

martin, the a3 move is more a joke than a real move. Than can be done becouse want to have some fun with some oponent that is not that much strong. Exept in some few cases in tournaments when the player wants to play blacks (becouse ready have something prepare) but have whites, so do something like a3 as a way to get arround and play the blacks opening he want to play, in this case i would no be surprice if the blacks answer the same, that is "no, no, no you are going to play whites".

But as far as I am corncer that move doesn't develop, doesn't get the center, and doesn't protect the king, so it is not really an opening it is just a move on the begining, and someone put the name "opening" to it. but it is not.

this makes me wonder, when the player is in front of the board  have 18 posible moves to be the first one, does each one of those have a name?

"Openings" consist of roughly the first 20 moves.

If your "opening books" don't get close to that number, you overpaid.

In a nutshell, the opening "is over" when you have developed your minor pieces and castled. Your goal (in the opening) is to "smoothly develop your pieces" and reach a playable middlegame.

Roughly 20/20/20 moves for the three phases of the game--opening, middlegame, endgame. That's a simple rule of thumb to start.

Unfortunately, most games end sooner than 60 moves, because of technical innaccuracies, outright mistakes, or draw agreements.

And (please) study all 3 phases, so you don't "feel lost" in a maze.  Jeremy Silman, "Complete Chess Strategy," (@1999) is as good a book as any, with which to start.

I think everything except maybe 1.d4 f6 has a name. 1. a3 is Anderssens Opening but 1.a3 - 2.h3- 3.c4 is 'The Creepy-Crawly' (Mike basman's idea).

I saw a definition that said 'the opening phase is over when the position on the board has not been seen before by at least one of the players'.