WSL Windows Subsystem for Linux
Microsoft's way of running Linux binaries on Windows. WSL1 (2016) translated Linux syscalls. WSL2 (2019) runs a real Linux kernel in a lightweight Hyper-V VM.
WSL2 is dramatically faster for filesystem-heavy work (npm install, git clone) thanks to native ext4. Cross-filesystem (Windows ↔ Linux) is slow though. Default Linux: Ubuntu, but Kali, Debian, openSUSE, Arch, NixOS available. WSLg adds GUI app support. WSL2 + VS Code Remote is the classic Microsoft development pipeline. The flip side: macOS does the same via Docker Desktop, Linux users avoid the whole problem.