The topic is probability

Probability is a branch of mathematics that quantifies the likelihood of an event occurring. It is expressed as a number between 0 and 1, where 0 indicates an impossible event and 1 indicates a certain event. The basic formula for the probability of an event $A$ is:

$$P(A) = \frac{\text{Number of favorable outcomes}}{\text{Total number of possible outcomes}}$$

For example, the probability of flipping a fair coin and getting heads is $\frac{1}{2}$, because there is one favorable outcome (heads) out of two possible outcomes (heads or tails).