An opening is properly the term for the first phase of a chess game (the other two being the middle-game and the end-game), and is generally regarded as completed when all of a player's back-rank pieces have been "developed" (ie. brought into play). An opening can take as few as 8 moves or as many as 20 to complete satisfactorily.

With the advent of the modern game however, sequences of successful opening moves were increasingly studied and developed by trial and error into principles and models of opening play that are now termed "openings" in general. At the same time names began to be used to describe the different openings for convenient reference (although the names rarely described the actual characteristics of each opening).

The actual number of possible openings is virtually limitless. White has a choice of 20 first moves (16 by pawn, 4 by knight) and Black has the same number of replies, making 400 different possible positions after only one move each. These figures rise to 72,084 different positions after two moves each (including en passant options), and more than 9,000,000 different possible legal positions after only three moves each!

All chess material tends to be organised genetically (ie. based on the sequential order of moves that created the position) rather than typologically (ie. based upon similarities of position reached). This makes knowledge of transpositions between openings particularly important, especially in the early stages of a game, as the ensuing move "position" (and any further variation that follows) is usually classified under the particular opening sequence most likely to have brought about the position.

There are no international rules governing the naming of openings, but a general convention or policy has grown to be accepted among all leading chess players and organisations over the years whereby recognised openings are (mostly) referred to by an identifying "name" combined with a "type" description.

Most openings are of one of the following "types":

Opening (a series of moves by White developed and tested in play) Defence (a passive or aggressive opening initiated by Black) System (a series of structural moves made by one side independently of the other) Game (older term for opening, now rarely used) Gambit (a sacrificial move by White) Counter-Gambit (always initiated by Black) Attack (an active threat initiated by White) Counter-Attack (always initiated by Black) Variation (any alternative line of play, often widely accepted over time)

The identifying "name" is usually (but not always) associated with either:

• The characteristics of the position (ie. the piece or tactic involved).
• The "inventor" (ie. first discoverer) of the tactical position.
• The analyst who first described the positional strategy in depth in a book or article.
• The player (often not the originator) who first used the opening in strong tournament play.
• The tournament where its repeated use popularised the opening.
• The city or country where a group of players developed the opening.

Lastly, one opening line may have many names (sometimes changing over time or according to country), while conversely one name may denote several openings.