Operand types
rel8(8 bits, signed. Represents a relative address from -128 to +127).rel16,rel32(16 / 32-bit, signed. Represents a relative address from –32,768 to +32,767 / –2,147,483,648 to +2,147,483,647 according to the operand size).imm8(8-bit, signed, Represents an immediate value. It is sign-extended to form a 16 or 32-bit immediate if it's combined with a 16 or 32-bit operand).imm16,imm32(16 / 32-bit, signed. Immediate value).r/m8(8-bit register or a byte from memory).r/m16,r/m32(16 / 32-bit register or value in memory, according to the operand size).m,m8,m16,m32,m64,m128(an operand in memory, expressed as a variable or array name, but pointed to by the DS:(E)SI or ES:(E)DI registers).m16int,m32int,m64int(integer operand in memory).ST(i)(the i'th element from the top of the FPU register stack (0 to 7), 0 by default).m32fp, m64fp, m80fporm32real, m64real, m80real) (floating-point operand in memory)m16:16, m16:32, m16:64(an operand in memory, segment:offset)
See the summarized table in JSON here.