MySQL GRANT PROXY - what does it mean?

I run: show grants for root@localhost; and I see GRANT PROXY ON ''@'' TO 'root'@'localhost' WITH GRANT OPTION From mysql docs: https://dev.mysql.com/doc/refman/5.5/en/proxy-users.html > This enables the external user to be a proxy for the second user; that > is, to have the privileges of the second user. In other words, the > external user is a “proxy user” (a user who can impersonate or become > known as another user) and the second user is a “proxied user” (a user > whose identity can be taken on by a proxy user). But I am not understanding what they mean. I got the system from another worker who left the job and want to make sure if everything is secure and do not know if this grant is even needed. But if it does not make any security issues, I can leave it. Can somebody explain in more simple way? **Update:** How can I connect as as another user? I was trying various combinations, of username password, but I cannot make it connect. For example I used user root, but password from another user, which did not work. Tried another user and root password, also did not work. **Update:** Or this maybe means that root user can connect as other user? How to do that at least for example if so?