• in GNOME Shell (host), virtual machine windows can't be moved unless clicking on another window, then moving the virtual machine window;
• in GNOME Shell (host), the Activities Overview can't be accessed if a virtual machine is focused;
• in Unity (host), clicking on an indicator while a virtual machine is focused results in the indicator menus not being displayed.

Here's a screenshot showing what happens in Unity when indicators are clicked while a VirtualBox 5.1.x virtual machine is focused:

npm is the default package manager for Node.js. It consists of a command line client that integrates with a remote registry, and it makes it easy to install, share and distribute code.

If you're using npm installed from a repository in Linux (like the official Ubuntu or Node.js repositories), you may have noticed that you can't install packages globally ("-g") as a regular user. Many websites mention installing npm packages using sudo, but this messes up some permissions and is not recommended.