RAM is an abbreviation for Random Access Memory. This is a sort of computer memory, that, different from other storage devices including hard disk drives or DVDs, allows the information to be accessed directly without reading the previous content located in it. Every time a program is started, it's stored inside the RAM, since it could be accessed considerably faster than if it was read from another media device. In terms of the hosting service itself, more RAM means that more web apps can run concurrently on a given server, especially if they're resource-demanding and are accessed by a great number of of people at the same time. Not like a shared web hosting package in which the system resources of a given account can be flexible and often depend on what other users consume also, a VPS offers a guaranteed amount of RAM which can be used always. That memory is allocated to one web server only and will not be used by other customers even in case it's not used.