Probability is a subtle concept that is typically defined in terms of the relative frequency of occurrence of an event, or the degree of belief that the event will occur (or that a statement is true, etc.).

Elementary probability
Sometimes introduced in primary school mathematics classes, the first serious study of the subject is usually undertaken in secondary school or university level courses
Probability theory
Formal, axiomatic study at the university level, based on real analysis and especially measure theory.

Major topics

See Wikipedia:Probability for more information.

Community content is available under CC-BY-SA unless otherwise noted.