RAM is an abbreviation for Random Access Memory. This is a sort of computer memory, that, unlike other storage devices including harddrives or DVDs, allows the info to be accessed directly without reading the previous content stored in it. Each time an app is started, it's stored inside the RAM, since it could be accessed considerably quicker than if it was read from another media device. With regards to the hosting service itself, more RAM means that more web apps can work all at once on a particular web server, especially if they are resource-demanding and are accessed by a significant number of people simultaneously. In contrast to a shared web hosting package where the resources of a given account could be flexible and sometimes depend on what other users consume as well, a VPS features a guaranteed amount of RAM which can be used at all times. That memory is allocated to one server only and shall not be used by other customers even if it's not used.