Your Deck (including Extra Deck and Side Deck) can contain up to 3 copies of a card that has the same name. However, certain cards have specific quantity restrictions that further limit the number that can be included in a Deck.
There are 3 types of restrictions: Limited cards are restricted to 1 copy in a Deck, while Semi-Limited Cards are restricted to 2 copies in a Deck. Forbidden cards are not allowed to be included at all.
The list of Forbidden and Limited cards is updated regularly. This list is applied to tournaments so please check it before participating: