If you tick this option you will be able to stay signed in to the website without the need to fill in your login details each time. This should last a number of days or until you select 'Logout'.
Two browsers may be signed in persistently at one time. Signing in a third browser will overwrite the oldest login.
When the 'logout' option is selected all concurrent logins are removed.
If you are on a shared computer do not tick this option or the next person to use the computer will be able to visit the website with your account.