RAM is an abbreviation for Random Access Memory. This is a sort of computer memory, which, 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. Whenever an app is started, it is stored in the RAM, since it can be accessed much quicker than if it was read from another media. With regards to the web hosting service itself, more RAM means that more web apps can operate at the same time on a certain server, particularly when they are resource-demanding and are accessed by a large amount of people all at once. Unlike a shared web hosting solution where the system resources of a given account may be flexible and often depend on what other users consume as well, a VPS provides a guaranteed amount of RAM which you can use all the time. That memory is assigned to one server only and won't be used by other customers even in case it's not in use.