WSL: Windows Subsystem for Linux

WSL (used to be "bash on Windows")  is now a simple command in Windows:
a portal to using alternative shells, and could use multiple different shells at the same time in separate windows.

The year of Linux on the (Windows) Desktop - WSL Tips and Tricks - Scott Hanselman

Install the Linux Subsystem on Windows 10 | Microsoft Docs

Windows Subsystem for Linux - Wikipedia

Microsoft's Windows Subsystem For Linux - More Details About How Bash On Windows 10 Works