Lexeme

A lexeme is an abstract vocabulary item whose different grammatical forms are treated as instances of the same item. It separates lexical identity from the particular form occurring in an utterance. An inflectional description can therefore connect several forms without treating each as an unrelated entry.^[ref]

For example, walk, walks, walked and walking can belong to the lexeme conventionally represented as WALK. Their differences involve inflection; forming a new item through derivational morphology is a different relation. A lemma is the conventional citation form used to label an entry, rather than the entire abstraction being represented.

This distinction matters when counting a text corpus. Counts of the exact form walked answer a different question from counts pooling all the specified forms of WALK. The grouping procedure must also handle ambiguous forms: spelling alone need not determine which lexeme a use instantiates.