An infix is an affix inserted inside a stem (an existing word). It contrasts with adfix, a rare term for an affix attached to the end of a stem, such as a prefix or suffix.
- The infix ‹iz› or ‹izn› is characteristic of hip-hop slang, for example hizouse for house and shiznit for shit. Infixes also occur in some language games.
- "Fucking" is sometimes used as an expletive infix, as in "un-fucking-believable". This can also be considered an instance of tmesis rather than an infix.
- The ‹ma› infix, whose location in the word is described in Yu (2004), gives a word an ironic pseudo-sophistication, as in sophistimacated, saxomaphone, and edumacation. This exists as a slang phenomenon popularised by Homer Simpson's use.