enantiotopic with respect to a methylene group would refer to a situation where if you changed either one of those protons to a different group then you would get enantiomers. The most common thing to see in NMR is diastereotopic protons. The idea is the same, but these occur when you have a chiral center in your molecule already, then if you were to change either of the two protons of a methylene to something else you would have diastereomers.