The VLT is the Very Large Telescope. That's the name given to the whole facility that consists of our four telescopes each with a mirror 8.2m across. Here, you see two of them, Melipal, which I work as a support astronomer for, and Yepun, which has a cool laser. In between them is the VST, which only has a 2.5m mirror, but VST is disappointingly not actually an acronym for Very Small Telescope, but instead means VLT Survey Telescope. It is used for large surveys, such as the VPHAS+, which I'm involved in and which is taking images of the Milky Way in the light emitted by hydrogen gas. VPHAS+ is a double nested acronym - it's the VST Photometric Hα Survey, so that would actually be the Very Large Telescope Survey Telescope Photometric Hα Survey.