Mature Industry
  
Well, certainly not the edutainment biz we work in.
A mature industry is one that is fully penetrated...in a G-Rated way. Think: the phone biz in America. Pretty much everyone who wants a phone now has one. Yes, they'll upgrade to fancier flavors of phone over time. But the market itself is mature. The hardware handset phone industry today is, eh, about $80 billion in sales each year. Next year it might be $82 billion, or $88 billion, or somewhere in that zone...but it won't grow more than 5 or 10 percent. A huge hit product might make it grow a bit more than that, and a soft economy might make it shrink.
"Mature" = not growing fast. Kinda like our ranges of humor in the jokes we make that teenage boys think are so funny.