Abstract
<jats:title>Abstract</jats:title> <jats:p>One of the most fundamental questions in vocabulary research is what “counts” as a “word,” or—given issues with defining what a word is—what counts as a “lexical item.” It influences frequency‐based word lists and word counts, automated indices in text analysis tools such as lexical diversity or sophistication, and target item selection in vocabulary assessments. This article explains and explores various ways in which words have been counted and grouped into counting units, such as types, lemmas, flemmas, and word families. It first introduces the relevance of deciding on a particular counting unit, particularly from the viewpoint of second language vocabulary acquisition and the notion of learning burden. It then presents various approaches and definitions of different counting units, before discussing advantages and challenges, or rather evidence‐based arguments for and against various units. It concludes with a caveat that these aspects need to be weighed up in terms of what a good clustering criterion and thus counting unit is for any particular context, purpose, and learner group so that the unit is both practical as well as valid and interpretable.</jats:p>