How about inflected forms like cats versus cat? These two words have the same lemma cat but are different wordforms. A lemma is a set of lexical forms having lemma the same stem, the same major part-of-speech, and the same word sense. The wordform is the full inflected or derived form of the word. For morphologically complex wordform languages like Arabic, we often need to deal with lemmatization. For many tasks in English, however, wordforms are sufficient.