Segment Override Operator (:...)
This operator instructs the assembler that the expression after the colon belongs to the segment given by the segment register name before the colon (CS, DS, SS, or ES).
XX = CS, DS, SS, or ES.
A memory reference with the value of the expression after the colon.
When a segment override is used in an instruction operand, the instruction will be prefixed by an appropriate segment override prefix instruction. This ensures that the indicated segment is selected.