Incircle, incentre, inradius

-An incircle is a closed plane curve whose points are equidistant from another point located inside it, called centre.

-An incentre is the point from which all points are equidistant.

-An inradius is a linear segment joining any point on the circumference or the surface of a sphere with its centre.

Link: https://www.youtube.com/watch?v=KEOa_WUoItY