untitled.fcpbundle

This is a FCP X library - it contains media, events, projects.

You probably stored it there unwittingly; libraries can be stored just about anywhere.

Double-click it to open in FCP X and see what it contains. You can also move it in the Finder, with FCP X closed. Of course, only trash it if you realized you don't want it.

That Library is the default library created when you first open FCPX 10.1. It actually should be in your Movies folder. It's size indicates you have at least one project or event inside with imported and/or transcoded media (the default "empty" size is about 156KB). You can safely move it to another hard drive and delete it (but not while FCPX is running.) To restart FCPX with that library available for use after moving it, double click on the library icon in the Finder. When you do that -- yet another (empty) Untitled library will appear in your Movies folder. You can Close that library in FCPX and that will keep it out of your way (right click on the Library in FCPX and select Close Library "Untitled" from the popup menu — just make sure it's the right "Untitled" library you're closing!)