RAM is an abbreviation for Random Access Memory. This is a type of computer memory, that, unlike other storage devices like harddrives or DVDs, allows the data to be accessed directly without reading the previous content stored in it. Whenever an app is started, it's stored in the RAM, as it may be accessed much faster 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 concurrently on a given server, particularly when they are resource-demanding and are accessed by a large amount of people concurrently. Unlike a shared web hosting solution where the system resources of a given account may be flexible and often depend on what other end users consume also, a VPS includes a guaranteed amount of RAM which you can use all the time. That memory is allotted to one hosting server only and shall not be used by other customers even when it is not in use.