Implied negativity in advertisements occurs when an advertisement criticizes the competition without ever actually naming it. This is in contrast to direct comparison ads in which the advertiser explicitly compares their product to that of a named competitor.
A good example of this kind of advertisement was Burger King’s ad campaign (this is some years ago now) that extolled the virtues of flame-broiled hamburgers in contrast to burgers that were simply cooked on a hot surface like a griddle. Burger King never mentioned McDonald’s in the ads, but it was clear that they were implying that McDonald’s hamburgers were of lower quality than their own because McDonald’s did not flame-broil.
A second example could be the recent ads for Macintosh computers. These ads portrayed the Mac as a hip young man while a stodgy, middle-aged man played the role of a PC. These ads did not attack any specific maker of PCs like Dell, but it was clearly implying that all makers of PCs made a product that was completely inferior to the Macintosh.