structure consisting of an artificial heap or bank usually of earth or stones

mound:

a small natural hill. however a mound can be artificial as well

a hill is bigger than a mound!

A hill is a landform which extends above the surrounding terrain in a limited area. Hills also have a distinct summit, although in areas with scarp/dip topography a hill may refer to a particular section of scarp slope without a well defined summit.

1- a natural elevation of the earth’s surface, smaller than a mountain

Mound :

1-a natural elevation of earth; a hillock or knoll

2-a heap or raised mass: a mound of papers; a mound of hay