An //immediate value// in [[Machine Language|machine code]] is a constant or literal value argument. For example, the 6502 [[Assembly Language|assembly]] instruction:

  LDA #$80

...will load the literal value 0x80 (128) into the accumulator (A register).

Note that the value to be loaded comes from an argument within the instruction stream; this contrasts with loading a value from a memory location in a data area, or from another register.