An administrator password (admin) is the password for any Windows account with administrative privileges.
In newer versions of Windows, such as Windows 11, Windows 10, Windows 8, and Windows 7, most primary accounts are configured as administrator accounts, so an administrator password is typically the password for your account. Not all user accounts are set up this way, but many are, especially if you installed Windows on your computer yourself.
All versions of Windows also have a built-in "Administrator" account that functions as an additional administrator account. However, this account is typically not displayed on the login screen, and most people don't even know it exists.
However, if you are using an older version of Windows, such as Windows XP, you may need this administrator password to access the Windows XP Recovery Console or when you attempt to boot into Windows XP Safe Mode.