With shared hosting, you’re sharing a server and that server’s resources with a bunch of other websites. With a VPS, you’re still sharing some resources because that’s determined by the hardware, but the software itself is set up in such a way that one machine acts like multiple different servers, providing a different virtual server for every user. For webmasters, using a VPS means that they get the administrative power of a dedicated hosting setup, including the ability to customize their server to suit them.