RAM is an abbreviation for Random Access Memory. This is a kind of computer memory, which, different from other storage devices including harddrives or DVDs, allows the information to be accessed directly without reading the previous content stored within it. Every time an app is started, it's stored in the RAM, because it could be accessed considerably faster than if it was read from another media. With regards to the hosting service itself, more RAM means that more web applications can run simultaneously on a particular server, particularly if they're resource-demanding and are accessed by a significant number of people at the same time. In contrast to a shared web hosting package where the system resources of a certain account may be flexible and quite often depend on what other users consume too, a VPS provides a guaranteed amount of RAM that can be used all the time. That memory is assigned to one web server only and shall not be used by other clients even if it is not being used.