The time of day when the sun is setting, when adults think it's too dark for kids to keep playing outside. The kids, however, insist there is still enough light out to keep playing for a while longer because it's not all the way dark yet. The adults think it's too dark out because they've been sitting in the house with lights on.
Mom yelling outside: "Kids, come inside. It's dark out there! Come in and wash, supper's almost ready!"
Kids: "Aw mom! It's not too dark out, we can still see the ball! It's only adult dark. 10 more minutes!"