what is an opening?????

Generally speaking, , an opening is defined by the introductory movs of a chess game. an  opening begins on move one. the obvious  question that suggests itself is surprisingly difficult to answer, how to we decide on what move an opening ends and the middlegame begins? there is no general agreement among players and authors about this, in many case it turns out to be a subjective judgement informed by playing experience. in this write i shall define openings (and their variations) as sequences of moves, that are specifically named. with the name in common chess usage and sometimes refering to a complex  of related positions. The advantage of using this convention is that we can know precisely at which move an opening or variation ends.  for instance the english opening is defined by single white move: 1. c4 the sicilian defence consist of 1 e4 c5. and the variation called the najdorf variation of the sicilian defence is delimited bye the moves  1. e4 c5, 2. Nf3 d6, 3 d4 cd4 4 Nd4 Nf6 5 Nc3 a6  by defining the word "opening" to designate move with name that are in general usage. we avoid dealing with such near-irrational sequences as a4 e5 2 f3, which do not  fall within the category  of opening as  i have define them. there are very few meaningful openings unnamed, but i shall touch upon them if the occasion arise.
most of writing is devided into major openings which can be identified within four move or fewer, for example, the ruy lupez  (1 e4 e5 2 Nf3 Nc6 3 Bb5) or the grinfield defence ( 1 d4 Nf6 2 c4 g6 3 Nc3 d5) etc. each of which then subdivide into variations. named variation of opening can be of allmost any length, for example, the closed variation of the sicilian defence has just two moves: 1 e4 c5 2 Nc3, and the exchainge variation of the ruy lopez (also known as the spenish game) consist of the four move 1 e4 e5 2 Nf3 Nc6 3 Bb5 a6 4 Bc6. lasker's variation of the queen gambit is distinguished by the seven moves 1 d4 d5 2 c4 e6 3 Nc3 Nf6 4 Bg5 Be7 5 e3 0-0 6 Nf3 h6 7  Bh4 Ne4      but some variation stem from other variations, which can stem from still others, and so forth. for example the chinese variation of the dragon sicilian evolves from this move-order e4 c5(this is sicilian defense.) 2 Nf3 d6 3 d4 cd4 4 Nd4 Nf6 5 Nc3 g6 (the moves thus far are know n as the dragon variation) Bc3 Bg7 7 f3 Nc6 8 Qd2 ( theese first eight moves define the yugoslav attack) 8 .... 0-0 9 Bc4 9some authers refer to this as the'Bc4 yugosalv attack') 9.....Bd7 10  0-0-0 and now with 10.....Rb8 (8), we have arrive  at the chinese variation of the dragon sicilian,