A cookie banner is the on-page notice a website shows to inform visitors about cookies and request or record their consent. It's how websites satisfy ePrivacy Article 5(3)'s prior consent rule — the term itself isn't in the law. Core components: informational text, "Accept All" and "Reject All" at equal prominence, a preferences panel, and a link to the cookie or privacy policy. EDPB, CNIL, and ICO guidance ban dark patterns — buried "Reject All" buttons, pre-ticked toggles, and cookies firing before any interaction. California's model differs — a "Do Not Sell or Share" link plus GPC honoring replaces the EU-style banner.