RAM, that means Random Access Memory, is a computer storage media which is accessed considerably faster than a hard disk, as the info can be read randomly, skipping the bytes before the needed information is reached. On a web server, the RAM is used to load scripts and web apps after they are executed, so the more RAM you can use, the more applications you'll be able to run at the same time and the more people will be able to surf your websites without effect on the site’s/server’s performance. Different from a disk drive, however, the RAM is employed for short-term storage purposes, as the info is lost when the power is shut off. When you use a shared web hosting account, the physical memory your scripts may use may be limited and may change based on what the other customers on the same machine use. Through a virtual or a dedicated hosting server, alternatively, you shall have a fixed amount of RAM which will not be used by others even when you don't use it at a particular time.