Tuples are not really a fundamental class, but are commonly used for a very fundamental purpose - multiple return values.
'TUP' names a set of parameterized immutable types called tuples, one for each number of parameters. Each has as many attributes as parameters and they are named 't1', 't2', etc. Each is declared by the type of the corresponding parameter (e.g. 'TUP{INT,FLT}' has attributes 't1:INT' and 't2:FLT'). It defines 'create' with an argument corresponding to each attribute.