In linguistics, a heteronym (also known as a heterophone) is a word that is written identically but has a different pronunciation and meaning.
In other words, they are homographs that are not homophones. Thus, row (propel with oars) and row (argument) are heteronyms, but mean (intend) and mean (average) are not (since they are pronounced the same).
Heteronym pronunciation may vary in vowel realisation, in stress pattern, or in other ways.