Strictly necessary cookies are the ones a website cannot function without: login sessions, shopping carts, security tokens, and load-balancing.
Third-party cookies are set by a domain other than the one you are visiting, usually by embedded services like ad networks, analytics tools, chat.
The ePrivacy Directive is the EU law that requires consent before storing or accessing information on a visitor's device, which is what makes cookie.
Prior consent means non-essential cookies and trackers must stay off until the visitor actively agrees. Consent given after scripts have already.