You have an idea. He starts to develop it, he works hard, but at some point he lacks resources, validations and sometimes even a space to make his idea definitely grow. This is the path that many entrepreneurs face in the process between having an idea and getting it off the paper.
This is what the incubators came to think of.
In medical vocabulary, an incubator is a place where a baby with growth difficulties will receive support to be able to develop in its most fragile moment. Entrepreneurship lent the concept and created environments where entrepreneurs with new ideas, still at an early stage, have the physical and practical-theoretical infrastructure to get an idea and take it to a first product or service model.