Probability simply means the likelihood of an event to occur and always takes a value between 0 and 1 (0 and 1 inclusive).
The probability of event A is denoted as p(A) and calculated as the number of the desired outcome divided by the number of all outcomes. For example, when you roll a die, the probability of getting a number less than three is 2 / 6. The number of desired outcomes is 2 (1 and 2); the number of total outcomes is 6.
Specifically, it quantifies how likely a specific outcome is for a random variable, such as the flip of a coin, the roll of a die, or drawing a playing card from a deck.