IB Maths AA 4.5 Definitions

The event that $A$ does not happen, written as $A'$, with probability $P\left(A'\right)=1-P\left(A\right)$.

The probability that one event happens given that another event has already happened, written as
$P(A \mid B) = \frac{P(A \cap B)}{P(B)}$ provided that $P(B) \neq 0$.

A set of outcomes from the sample space.

Describes events that cannot happen at the same time, so $P\left(A\cap B\right)=0$ and $P\left(A\cup B\right)=P\left(A\right)+P\left(B\right)$.

One possible result of a trial.

Measures how likely an event is to happen, taking a value between $0$ and $1$, where $0$ means impossible and $1$ means certain.