can read Foxhelp its well explained (search for "return command")
or also https://msdn.microsoft.com/en-us/library/512x8ss9%28v=vs.80%29.aspx
can see all possbilities for return command

lnReturn Specifies the expression returned to the calling program.

return (lnReturn) replaces maybe the old macro "return &lnReturn" .it evaluates the expression returned to the calling programm.
it can be at the end of a procedure or function or even a modal form..