What is the marginal rate of substitution MRS and why does it diminish as the consumer substitutes one product for

What is the marginal rate of substitution (MRS) and why does it diminish as the consumer substitutes one product for another? Use examples to illustrate.
Guided Response: In 300 words or more, please, provide your response to the above discussion question. Find two goods from your own consumption basket and explain how the MRS changes for the two products as you substitute one for the other.