Multiple sign-in: Definition
Multiple sign-in helps you manage more than one account at the same time, which saves time, and makes it easier to compare them.
You can sign in and switch between multiple Google Accounts at the same time, in the same browser. For example, you can have both your Google AdWords accounts and your personal Gmail open at the same time.
You can also use one Google Account to manage up to 5 different AdWords accounts.