Tarot decks have 78 cards... 22 Major Arcana cards and 56 Minor Arcana cards... The Minor Arcana can either be 'pips' or 'scenic'...
Oracle decks can have any number of cards, have no major or minor arcana per se, and follow whatever so-called 'rules of interpretive and/or fixed divination' that the author of the deck sets up...
Tarot decks, to me, follow a much more structured format than Oracle decks, altho both can, and are, used very intuitively by many readers...
I use both kinds of decks, enjoy them, and get great readings from them... I use Tarot mostly for readings and incorporate the Oracle decks as an adjunct to the readings...