Definition:Elementary Event

Definition
Let $\mathcal E$ be an experiment.

An elementary event of $\mathcal E$, often denoted $\omega$ (Greek lowercase omega) is one of the elements of the sample space $\Omega$ (Greek capital omega) of $\mathcal E$.

Also known as
An elementary event is one of the possible outcomes of $\mathcal E$.

Thus outcome means the same thing as elementary event.