If you are a person like me who uses your gmail account from many places and sometimes forget to log out the session.
or session is not closed due to some reason.
But, just dont worry gmail has a "Remote Logout" or "Sign out all other sessions" option.
Just scroll down to the gmail.
In the end you will find something like this
"Last account activity: 26 minutes ago on this computer.  Details"

Click on Details.
It will show you the list of ips from where this account was used.
you can click on "Signout all other session" and you are done.

Your all open sessions will be logged out, if any.