Expressions in specification and programming languages often extend algebraic terms by additional term formation rules and enlarged evaluation domains. For use in different contexts, the semantics of these expressions must allow for interface modification, that is, evaluation must be compatible with signature translation and with variable renaming. This work introduces term charters as an abstract framework for terms and expressions following the slogan “evaluation is invariant under change of notation”. Several examples illustrate the use of term charters. Different term charter representations are discussed and morphisms between term charters are defined. Finally, the relation of term charters with institutions in general and with context institutions in particular is demonstrated.