This keyword is used for introducing a procedure declaration.

It is a synonymous for PROCEDURE.

[ STATIC ] { PUBLIC | PRIVATE } { PROCEDURE | SUB }
  Identifier
  (
    [ Parameter AS Datatype [ , ... ] ] [ , ]
    [ OPTIONAL Optional Parameter AS Datatype [ , ... ] ] [ , ] [ ... ]
  )
  ...
END

This declares a procedure, i.e. a method that returns nothing. To return a value, use FUNCTION

The END keyword indicates the end of the procedure.