RAM, that is short for Random Access Memory, is a computer storage media that is accessed faster than a hard drive, simply because the data can be read randomly, skipping the bytes before the needed data is reached. On a server, the RAM is employed to load scripts and web apps when they are executed, so the more RAM you may use, the more apps you'll be able to run simultaneously and the more people shall be able to look through your sites with no effect on the site’s/server’s performance. Unlike a disk drive, however, the RAM is employed for momentary storage purposes, as the information is lost the moment the power is shut off. When you use a shared web hosting account, the physical memory your scripts could use may be limited and may change according to what the some other clients on the same hosting server use. With a virtual or a dedicated server, however, you shall have a guaranteed amount of RAM that will not be used by anybody else even if you don't use it at a particular time.