This document discusses subroutines and the CALL and RET instructions used to implement them in the 8085 microprocessor. It defines a subroutine as a group of instructions written separately from the main program to perform a function that occurs repeatedly. The CALL instruction transfers the program sequence to the subroutine and saves the return address on the stack. The RET instruction inserts the return address from the stack into the program counter to return to the main program. When CALL is executed, the stack pointer is decremented, and when RET is executed, the stack pointer is incremented.