WARNING
This article uses Unofficial terminology.
A term is a syntactic element of a formula. Each term has a data type that defines what operations can be performed on it.
Lambda term
Main article: Lambda term
Lambda terms are first-class. They can be passed as arguments to other functions, returned from other functions, and be assigned to variables. They are comprised of |literals and LAMBDA functions.
Primitive function
Primitive functions are not first-class and comprise every default function. The only operation that can be performed on primitive functions is application (e.g. applying them to lambda terms, such as SUM(1, 2, 3)).