Usr/bin/env

[Julius Hamilton]

At the top of a script I see "#!/usr/bin/env sh".

I was curious, what software system is this a part of? Bash, Linux, or
Unix? I.e., I assume the shebang is common to various shell languages,
bash, zsh, etc. "Sh" is a shell chosen. But if I wanted to know more about
this directory, "/usr/bin/env", what is this concept's original location?
Does this filesystem structure go back to Unix? Or is Unix no longer
commonly used so I should turn to the Linux documentation?

Thanks very much,
Julius