The term “game mechanic” is often used when discussing games, but are we all talking about the same thing? While game studies and related fields have produced several notable definitions, there is currently no accepted standard for the term within the broader community. Through a systematic literature review spanning six academic venues and several prominent books, we identify and analyze 49 explicit definitions for the concept of “game mechanics”. Though some of the definitions are similar, they are all fundamentally distinct. Our work demonstrates the importance of providing or citing a definition when discussing game mechanics, and we provide a wide range of options to choose from.