A tuple type is a comma-separated list of types, enclosed in parentheses.
This list of types also can have name of the elements and use those names to refer to the values of the individual elements.
An element name consists of an identifier followed immediately by a colon (:).
Common use -
We can use a tuple type as the return type of a function to enable the function to return a single tuple containing multiple values
Tuples are considered value types. More info on tuples could be found in the documentation: developer.apple.com/library/content/documentation/Swift/Conceptual/Swift_Programming_Language/TheBasics.html