What is Ad Creep?

Legal Definition
Ad creep refers to the increased "creep" of advertising into previously ad-free spaces. The earliest verified appearance of the term is in a 1996 article "Creeping Commercials: Ads Worming Way Into TV Scripts" by Steve Johnson for the Chicago Tribune, however it may have been coined by a subscriber to Stay Free! magazine, according to another source.

While the virtues of advertising can be debated, ad-creep often especially refers to advertising which is invasive and coercive, such as ads in schools, doctor's offices and hospitals, restrooms, elevators, on ATMs, on garbage cans, on vehicles, on restaurant menus, and countless other items. In Steve Johnson's piece referenced above, he criticizes product placement and "creative advertising enhancements" as "one more manifestation of an environment in which the commercial assault is almost nonstop". Commercial Alert, a nonprofit organization founded by Public Citizen "to keep the commercial culture within its proper sphere, and to prevent it from exploiting children and subverting the higher values of family, community, environmental integrity and democracy" also characterizes "ad creep" as an assault, with ad companies fighting a "relentless battle to claim every waking moment, and what one executive called, with chilling candor, mind share".

On the other hand, modern advertisers are compelled to react to changes in consumer habits. A New York Times article notes that "consumers’ viewing and reading habits are so scattershot now that many advertisers say the best way to reach time-pressed consumers is to try to catch their eye at literally every turn." And, the article suggests that ad agencies believe that as long as ads are entertaining, people may not mind the saturation. As people have turned from traditional media, advertisers have not only struggled to create brand awareness, but there is also a move to "microtarget people at precisely timed moments" as well, according to an article in Stay Free!.

Occasionally, the term "Ad Creep" has been used to describe a process of slowly infusing more ads into places where ads have been expected (television shows, for example) such as in this 2011 Advertising Age article describing the increase in both the time devoted to ads and the number of ad messages in the Super Bowl. This is not a standard use of the term, but it is related.
-- Wikipedia