Probability is a branch of mathematics that deals with numerical descriptions of how likely an event is to occur or how likely it is that a proposition is true. The probability of an event is a number between 0 and 1, where 0 indicates the impossibility of the event and 1 indicates certainty. The higher the probability of an event, the more likely it is that the event will occur.

To calculate the probability of an event, we need to know the total number of possible outcomes and the number of favorable outcomes. The probability of an event is equal to the number of favorable outcomes divided by the total number of outcomes.

Probability can be used to predict how likely events are to happen, and it is often used in real-world applications such as insurance, finance, and science. Probability can be theoretical, dealing with probabilities in a purely theoretical setting, or empirical, dealing with probabilities in the context of real experiments.

Some key concepts related to probability include sample space, which is the set of all possible outcomes of an experiment, and event, which is a subset of the sample space. The probability of all the events in a sample space adds up to 1.

In summary, probability is a measure of the likelihood of an event to occur, and it is expressed as a number between 0 and 1. To calculate the probability of an event, we need to know the total number of possible outcomes and the number of favorable outcomes. Probability is used in various fields to predict how likely events are to happen.