IAB is an abbreviation of Interactive Advertising Bureau. This is the trade association for digital advertising and marketing. They set the standards for, among other things, the dimensions of display banners. An IAB banner set is a banner set that consists of 5, 6 or 7 banners in one of the sizes below:

300×250 – rectangle
336×280 – large rectangle
120×600 – skyscraper
300×600 – wide skyscraper
160×600 – large skyscraper
728×90 – leaderboard
970×250 – billboard
468×60 – banner
320×50 – leaderboard mobile