RAM is an abbreviation for Random Access Memory. This is a type of computer memory, that, unlike other storage devices such as harddrives or DVDs, allows the data to be accessed directly without reading the previous content saved within it. Anytime an app is started, it's stored in the RAM, because it could be accessed much quicker than if it was read from another media. With regards to the web hosting service itself, extra RAM means that more web applications can work simultaneously on a given web server, especially when they are resource-demanding and are accessed by a large amount of people concurrently. In contrast to a shared web hosting plan where the resources of a given account could be flexible and quite often depend on what other users consume as well, 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 if it's not being used.