displacement
A fixed number added inside a memory operand, such as the 8 in [rbp - 8] or ldr x0, [x1, #8].
A displacement (offset) is a signed constant encoded in the instruction and added to the base (and scaled index) to form an effective address; x86-64 allows 8 or 32 bits, ARM64 a scaled unsigned 12-bit or signed 9-bit field, RISC-V a signed 12-bit field.
Examples
In
mov eax, [rdi + 12], 12 is the displacement: a field 12 bytes into the structrdipoints at.