What and how Transient Designer can be used

Hello, my name is Jason and I happen to come across the word Transient Designers in a magazine after hearing a friend of mine used it in his speech on sound production. I have not had the opportunity to look really for the possible simplest but detailed meaning to the word “Transient Designer” and therefore would be happy to know what a Transient Designer is? And also to have the best guidelines that can one follow to use the Transient Designers in various mixes during an event such as a musical concert? Thank you.
