Diastereotopic Definition:

Diastereotopic are Nonequivalent protons for which the replacement test produces diastereomers.

Diastereotopic Explained:

When having two hydrogens attached to one carbon it has 3 types of conditions and one of them is a diastereotopic one. When hydrogen for instance switches its position with another bond to form an alkene, and if there is another hydrogen on the other side that looks similar yet not mirroring, this similarity is referred to as diastereotopic.