A Chromium session is the authenticated browser state stored by Chromium-based browsers such as Chrome, Edge, and Brave. It is usually maintained with cookies, session tokens, and related local data that tell a website the user is already signed in. As long as those artifacts remain valid, the browser can keep access without requiring the password again.
This matters in cyber security because stealing a session can be just as useful as stealing credentials. Infostealers and browser-theft malware often target cookies and tokens to bypass multi-factor prompts and reuse a logged-in identity from another device. Defenders look for signs of session abuse such as unexpected logins, impossible travel, unusual browser profiles, or token reuse from new endpoints. Reducing the lifetime of sessions, revoking tokens after compromise, and protecting browser data on the host all help limit the damage.