Kinds are types for types. Kinds are simple, having a name and potentially some parameters. Types have exactly one Kind. Terms can have multiple Types, so they can have multiple Kinds. Types are attached with a single colon. Kinds are attached with a double colon. There are 3 builtin Kinds: Term, Constant, and Nil. New kinds do not need to be defined before they are used.

5 : Prime :: Term;
2 : Second :: Unit;
1 : [1] :: Constant;
3 : [3] + Integer + Second :: Constant + Term + Unit;