Indexed Addressing Mode:
Indexed addressing mode is a type of addressing mode used in computer architecture where the effective address of the operand is obtained by adding a constant value or a value stored in an index register to the base address. The base address is typically stored in a general-purpose register, while the constant or index register holds the offset.

Explanation:
When the offset of the operand is stored in one of the index registers, it is referred to as indexed addressing mode. This means that instead of directly specifying the memory address of the operand, we use the value stored in an index register to calculate the effective address.

The index register contains a value that is added or subtracted from the base address to obtain the final memory address of the operand. This allows for more flexible addressing, as the offset can be dynamically adjusted based on the needs of the program.

Benefits of Indexed Addressing Mode:
1. Flexibility: Indexed addressing mode allows for flexible memory access by using a dynamic offset. This is particularly useful when working with arrays or data structures where the memory locations may not be known in advance.

2. Efficient Memory Access: By using indexed addressing, the effective address calculation can be done in the CPU itself, reducing the number of memory accesses required. This can improve the overall performance of the system.

Examples:
Let's consider an example to understand how indexed addressing mode works:

Suppose we have a base address stored in register R1 and an offset stored in index register R2. To access the operand, we would perform the following steps:

1. Load the base address from R1.
2. Add the offset value from R2 to the base address.
3. The result is the effective address of the operand.

This allows us to access memory locations that are not directly specified in the instruction, making the indexed addressing mode a powerful tool in computer architecture.

Conclusion:
In conclusion, when the offset of the operand is stored in one of the index registers, it is referred to as indexed addressing mode. This mode allows for flexible and efficient memory access by using a dynamic offset value. It is commonly used in computer architecture to access data structures and arrays.