The following information and links explains about the The Local System Account.
What is NT Authority\System (Local System) account?
Is it a part of Authenticated Users ??
Service running in local system account. Will it be able to access the AD/GP objects which are only accessible to Authentticated users?
The Local System account is a powerful account that has full access to the computer. The actual name of the account is NT AUTHORITY\System. The Local System account does not have any rights to access the network. When network access is necessary, Local System uses the account Domain\computername$.
With the release of Windows Server 2003, two new built-in account types similar to Local System were added: the Network Service account and the Local Service account.
Read the below articles for more information: