The Free On-line Dictionary of Computing (30 December 2018):

return from interrupt

    (RTI) An instruction mnemonic on many
   computers including the 6502 and 6800.  The variant "RETI"
   is found among former Zilog Z80 hackers (almost nobody
   programs these things in assembly code anymore).  The Intel
   80x86 equivalent is "IRET".

   (1994-10-31)