Is "NT AUTHORITYSYSTEM" an user or a group?

At the windows System is displayed with the group symbol: . Also resolving it with Win32 LookupAccountSid retus SidTypeGroup.

On the other hand processes can run in the system context like in an user context. Also Microsoft documents describe it as "system user" or "system account", and not as "system group".

Is it a user which is for any legacy purposes displayed as group?

(Or is it something Weer Heisenberg would have been interested in?)

Edit This question ist not about what system should be used for. It is about why is system displayed and inteal resolved as group but behaves like an user.