From The TV IV
Pop-up advertisements have been used by television since the early new millennium. These ads appear during the program, usually at the top or bottom of the screen, and usually advertise other on-network programming. The ads can range from transparent and insignificant, to intrusive and distracting. Pop-ups are sometimes complained about as they have been known to obscure important action during a program.
While most network TV and cable networks have resorted to using pop-ups, a few networks, such as Adult Swim, still do not use them.