The type (A,B) is a type for binary tuples (pairs) of values, one of type A and another of type B. The type (A,B,C) is a triple, and so on.
The type (A) is the same as the type A and is not considered a tuple.
The nullary tuple type () is the type of the unique value also written () and is pronounced “unit”.
In the standard Unison syntax, tuples of arity 2 and higher are actually of a type Tuple a b for some types a and b. For example, (X,Y) is syntactic shorthand for the type Tuple X (Tuple Y ()).
Tuples are either constructed with the syntactic shorthand (a,b) (see tuple literals) or with the built-in Tuple.Cons data constructor: (a, b).