Wikipedia has an article about Yu-Gi-Oh! Trading Card Game.

Yu-Gi-Oh! Official Card Game is the version of the Yu-Gi-Oh! card game manufactured by Konami. It is played mainly in Japan and parts of Asia. The OCG is printed in Japanese and Korean. It has previously been printed in English (referred to as Asian-English) and has also had 3 different Chinese prints of cards, including two "Blue-Eyes White Dragons" and a "Dark Magician".

Generally, the legal status of a card is the same in the Japanese version of the game as it is in the Advanced Format, since the Advanced Format is designed for international tournaments. However, there will occasionally be a card Forbidden in the Japanese cardlist, and be outright Illegal in the TCG.

With the exception of TCG only cards, TCG cards are legal in OCG tournaments. Due to the cards having different backings, if a player chooses to use a mixture of OCG and TCG cards, they must use protective sleeves that cover the back of the cards. However in some parts of Asia, local sanctioned tournaments have restricted the use of TCG cards.

OCG tournaments are divided into three classes: Expert, which has no age restriction, Regular: for secondary school students and Challenge, for primary school students.