From Teflpedia

A lexeme (/leksi:m/) is a unit of morphological analysis in linguistics. It corresponds roughly to the set of forms taken by a single word. It differs from the listeme in that the latter refers to the different uses a word might have.

In the case of a dictionary entry, the headword, or lemma, might be followed by the lexemes of that lemma.

Lexemes are governed by rules of grammar.

Lexemes can be composed of smaller units with individual meaning called morphemes.