Let $P$ be a polygon.
Let $C$ be a circle which is inscribed within $P$.
Then $C$ is an incircle of $P$.
The center of an incircle of a polygon is called an incenter of the polygon.
A radius of an incircle of a polygon is called an inradius of the polygon.
In the above diagram, $OG$ is an inradius of the polygon $ABCDEF$.