# How long is an eon in years?

Eon has a number of meanings. In Astronomy, an eon refers to 1 billion (${10}^{9}$) years. But it also refers to a very long, unspecified period of time, or specific geologic stages of the Earth.
Since this question is posted in Astronomy, I will assume that the answer of eon = ${10}^{9}$ years is the most appropriate, however it is not the most common.