5 seconds of our life wasted while trying to watch the 11-hour version of Pink Fluffy Unicorns. Also is your excuse when caught watching something you shouldn't be seeing.

the whale tail is the shape formed when a g-string rides up high over a womans trousers

A piece of advertising. At first it was called advertisement, afterwards advert, and now just ad. They are very common in the internet. They can be displayed as popups, popunders, banners, skyscrapers, text ads and in many other ways.
Some companies exploit them as adware - programs that advertise on the computer they are installed on. Normally the user doesn't know that they're installed until seeing the first ads. Although, most people avoid using such over-advertised products because they have no interest in supporting such companies that exploit adware.
Some web browsers, like Firefox, have the ability to have add-ons installed. Such add-ons include ad blockers like Adblock Plus, that help the user remove unwanted flash, text, picture, and whole frame ads. For other browsers, users can install additional software that remove ads.

AD is an abbreviation for "act dumb", this is when someone tries to act like he/she does not know what it going on despite the fact that they know well what is really happening. This is common among dumbasses who try to look cool and act gullible and dumb around girls

Anno Domini, Latin for "in the year of our lord". AD marks the years after the birth of Jesus Christ.

For politically correct reasons, AD is being replaced by CE.

Is an acronym for Anti-Depressant. AD, . ,

Short for the too short-lived show Arrested Development formerly on Fox.