This is a French culinary term meaning "everything in its place," and refers to the arrangement of supplies at a cooking station. The idea is that there is an ideal configuration of pots, pans, knife, raw food, etc. for the dishes you are preparing. So rather than thrashing back and forth with lots of wasted movement (Muri, muda?) everything should be set up correctly from the start, saving time and energy.

The term has also been used in more extended way to refer to a state of mind, and the organization of other systems.

According to work-clean-dan-charnas, notable features of good mise-en-place include the following:

What is good mise-en-place for software engineering?