RAM is an abbreviation for Random Access Memory. This is a kind of computer memory, that, different from other storage devices like hard disks or DVDs, allows the data to be accessed directly without reading the previous content stored inside it. Each time an application is started, it is stored inside the RAM, as it could be accessed much quicker than if it was read from another media device. In terms of the hosting service itself, extra RAM means that more web apps can run at the same time on a particular hosting server, particularly when they're resource-demanding and are accessed by a great number of of people all at once. Different from a shared web hosting plan where the system resources of a certain account could be flexible and quite often depend on what other end users consume also, a VPS has a guaranteed amount of RAM which can be used at all times. That memory is allotted to one hosting server only and won't be used by other clients even in case it is not used.