What is diminishing marginal rate of technical substitute?

The diminishing marginal rate of technical substitution (MRTS) refers to the rate at which one input can be substituted for another while maintaining the same level of output, decreasing as more of one input is used. It reflects the principle that as you increase the use of one input (e.g., labor), you will need to give up increasingly larger amounts of the other input (e.g., capital) to maintain the same output level. This concept is fundamental in production theory and helps illustrate the trade-offs producers face in input combinations.