[yakk0]

it's the subsystem for running Linux. It's not actually Linux, and after enabling the subsystem you still have to actually get the Ubutntu image. That image is the Linux part.

[Someone1234]

We all understand how it works. Repeating that is unconstructive.

It is a bad name that is bad English. It was bad when it was "Windows Services for UNIX" too as an aside.

[JdeBP]

Note that this subsystem never actually was "Windows Services for UNIX". That was another subsystem, another personality on top of the Windows NT kernel.

[Someone1234]

Per context, "it" was the name of the thing. "It" (the name) was a bad name then and is a bad name now.