Into the great wide open 
Under them skies of blue 
Out in the great wide open 
A rebel without a clue…
(Tom Petty and the Heartbreakers)

Void is something like the no-type: it says 'there is, or will be, absolutely no data'. This is used as return value for functions which don't return anything. See The Syntax of Functions:

“…functions which do not return anything [of] the type of the return value is void. When putting such functions to use in a step, simply omit the 'void' keyword. In turn, functions WITH a return value are usually used exactly BECAUSE of this value, and used accordingly.”