Then you should know what browser profiles are.
Browser profiles is a way to separate usage of the web browser per user. Just like any login system but without password. That means history, cache, cookies and as a result logins will be scope to a single user.
This is ideal when you are testing website for different logins at the same time or just want to separate work and personal browsing history.
Separation of browsing history might get more important with time as it's emerging trend for search enginge to personalise search results.
Most popular browsers have browser profiles built in already: