Banner advertising is an important form of online marketing that involves graphical images displayed at the top of web pages. It is effective for increasing brand awareness and generating website traffic in a cost-effective manner. Common banner types include pop-ups, pop-unders, and animated or expanding banners, though some of these can be intrusive for users. Key metrics for measuring banner performance include click-through rates, cost per thousand impressions, and return on investment. Legal and ethical issues also need consideration to avoid deceptive or misleading advertising practices.