A body is said to be homogeneous if the substance of any part of it is indistinguishable from any other part.
Just to specify that a body is made of the same substance throughout is not an adequate definition.
For example, a column of air in the atmosphere is denser at the bottom than at the top.
The fact that it is "all made of air" is one thing, but the air at the bottom can be distinguished from that higher up because the densities are different.
Thus a column of air is not homogeneous.
The opposite of homogeneous is heterogeneous.