NASM 2.05 based x86 Instruction Reference[ch298]
A.5.274 RET, RETF, RETN: Return from Procedure Call RET ; C3 [8086] RET imm16 ; C2 iw [8086] RETF ; CB [8086] RETF imm16 ; CA iw [8086] RETN ; C3 [8086] RETN imm16 ; C2 iw [8086] - RET, and its exact synonym RETN, pop IP or EIP from the stack and transfer control to the new address. Optionally, if a numeric second operand is provided, they increment the stack pointer by a further "imm16" bytes after popping the return address. - RETF executes a far return: after popping IP/EIP, it then pops CS, and _then_ increments the stack pointer by the optional argument if present.