Quoting from the standard:
7.4.2.7 include/1
If F is an implementation defined ground term designating
a Prolog text unit, then Prolog text P1 which contains
a directive include(F) is identical to a Prolog text P2
obtained by replacing the directive include(F) in P1 by
the Prolog text denoted by F.
Example:
:- include("hello.pl").
This addresses #583 and #634.