Session
A user's ongoing interaction with a site — usually a server-side object with an ID mapped via a cookie.
When you log in, a session ID is generated, stored on the server (in memory, Redis, or DB), and sent to the browser as a cookie. On every request the server checks the session ID and knows who you are.
Different from JWT-based authentication: JWT stores everything in the token itself; sessions store only the ID in the token.