Definition of offsuit
offsuit means that two cards are not of the same suit. Suit refers to the four suits of the four families of the classic 52-card deck (heart, spades, clubs and diamonds), so if you receive an ace and a king in spades, your cards are said to match. If you receive an Ace in Spades and a King in Clubs, your cards are considered to be offsuitth. Any combination that is not spades, heart-heart, diamonds-tiles or clubs and clubs will be considered offsuitth.
Offsuit cards vs. matching cards
If you've ever played poker before, you know that as a general rule, people like matching cards. Although you shouldn't overestimate them either, it's true that matching cards will give you an advantage over cards that are not matched. For example, let's take a hand like 8-9 offsuit and compare it to a hand like 8-9 matching. We will calculate the fairness of each hand against a random hand. 8-9 offsuit will have a 48% equity against a random hand, while a hand like 8-9 Match will have a 51% equity. In the long run, this is the difference between losing a little or winning.