Functional cookies support non-essential website features beyond basic operation — remembering user preferences, chatbot state, embedded video settings, social sharing widgets. They cover a broader category that often includes customization cookies (user-chosen settings like language and theme) as a sub-type. Under GDPR and ePrivacy Article 5(3), functional cookies generally need opt-in consent — the ICO and EDPB take a narrow view of strictly necessary, and "improves user experience" isn't enough. A common misclassification is treating chatbot or personalization cookies as functional-and-therefore-necessary. Under CCPA, functional cookie data usually stays out of the sale/sharing definition unless shared with third parties.