It’s a tiling window manager that has been popular in ricing community. Window manager is a subcomponent of a desktop environment (eg. KDE has KWin), so I suppose you can say it is lighter, but it’s different from desktop environments, which has window manager alongside many other components.

As the name suggests, all it does is manage windows. You can move them around, make one take up the whole screen, move them into different workspace, etc. What makes it popular is that it’s minimal, making it easier to build your own desktop environment, and a perfect fit for keyboard-oriented workflow. I use Hyprland myself, and I can definitely work just fine without mouse.