An infix is a type of affix that is inserted inside of a stem or base. Infixes may introduce new information to the base, specifically relating to grammatical functions like tense, number, aspect, and so on.
Gibson, J. A. (1973). Shuswap grammatical structure. [Doctoral dissertation, The University of Hawaii].
Suttles, W. (2004). Musqueum reference grammar. UBC Press. SFU Student Access.