The term “jihadism” is popular, but difficult. It has narrow senses, which are generally valuable, and wide senses, which may be misleading. This article looks at the derivation and use of “jihadism” and of related terms, at definitions provided by a number of leading scholars, and at media usage. It distinguishes two main groups of scholarly definitions, some careful and narrow, and some appearing to match loose media usage. However, it shows that even these scholarly definitions actually make important distinctions between jihadism and associated ideology. The article closes with a warning against the risks of loose and wide understandings of such important, but difficult, terms.