A based-indexed operand is like a based operand, except it specifies one additional register called an index register. The sum of the displacement, the value of the base register and the value of the index register becomes an effective address. The value of the effective address is the operand.
The following instruction is an example:
The source operand in this example is the value located at an effective address that is the sume of 2, the value of ebx and the value of edx.
Note that it is possible to specify no base register. In this case, the value that the base register supplies is zero. Here is an example: