RAM is an abbreviation for Random Access Memory. This is a kind of computer memory, which, unlike other storage devices such as harddrives or DVDs, allows the information to be accessed directly without reading the previous content located inside it. Whenever an app is launched, it's stored inside the RAM, since it can be accessed much more quickly than if it was read from another media. With regard to the website hosting service itself, more RAM means that more web apps can work simultaneously on a particular hosting server, particularly when they're resource-demanding and are accessed by a large number of people concurrently. Different from a shared web hosting plan in which the resources of a particular account can be flexible and often depend on what other users consume too, a VPS provides a guaranteed amount of RAM which can be used at all times. That memory is allocated to one hosting server only and will not be used by other customers even when it's not in use.