There is a standard number for most Tarot Decks of 78 cards. Sometimes a deck is what is called a "Majors Only" Deck which only has the 22 cards of the Major Arcana.
A full deck also has an extra 56 cards. These are in four suites.
In each suite are cards numbered 1 thru 10 and 4 court cards featuring royal personages in them.
Oracle decks are different and usually come with a single particular explanation for each card as opposed to being more interpretaive in the case of tarot cards.
Unlike Tarot cards, Oracle decks can have as many cards as their creator desired.