Definitions without jargon walls
A cookie is a small text file or binary slot stored on your device, set either by us (first-party) or by a partner whose script loads on our pages (third-party). Pixels (sometimes called trackers) load as tiny images or scripts and can work together with cookies to measure whether an email or advert contributed to a visit.
Similar technologies include HTML5 local storage, session storage, service-worker caches when used to remember identifiers, and server-set identifiers echoed in headers. We only discuss them here when they behave like cookies for privacy purposes.