# What is a vocabulary in logic

I am reading notes on finite model theory and I came across a notion of a vocabulary. What is it? I tried searching on the internet but did not find anything relevant.

• The non-logical symbols of the language, also called signature or vocabulary. – Mauro ALLEGRANZA Sep 29 '18 at 11:00
• Also called a language. We have way too many names for some things. (@MauroALLEGRANZA You should turn your comments into an answer.) – Noah Schweber Sep 29 '18 at 19:45

Definition 2.1 A vocabulary $$σ$$ is a collection of constant symbols (denoted $$c_1,\ldots, c_n,\ldots$$), relation, or predicate, symbols ($$P_1,\ldots,P_n,\ldots$$) and function symbols ($$f_1,\ldots,f_n,\ldots$$). Each relation and function symbol has an associated arity.