WSL is a full Ubuntu operating system that you can install on your Windows 10 machine.
Please keep in mind that this is beta software. This means that any part of it is subject to change, as feedback is collected and improvements are made based on community feedback.
In fact, if you have any issues you run into you, you can open a GitHub issue with Microsoft to let them know about it!
Microsoft's Creator's Update includes some improvements to the WSL that are not included in the regular release of Windows yet. The biggest one being that you can launch Windows programs from WSL.