# What is a non-elementary event in Probability?

An elementary event is an event which contains only a single outcome in the sample space.

For example, if a coin is tossed twice, S = {HH, HT, TH, TT}. Then, {HH}, {HT}, {TH} and {TT} are elementary events.

What is a non-elementary event? Please, give examples.

A non-elementary event is an event that is not elementary, i.e. a subset that contains more than (or less than) one element. For example, from the same $S$, you could have $\{HH,TH\}$.
This in contrast to e.g. $\{HH,TH\}=\{HH\}\cup\{TH\}$ wich is not elementary.