its a part of you hard drive that is used as memory when you are running low on ram.its slower than ram because its on a spinning hard drive.
what operating system and how much ram do you have? click control panel/system to find out if unsure.
ram is reasonably cheap and is easy to upgrade if your motherboard can take more.512 of ram is a decent ammount nowdays if using xp.
if xp try clicking: start/control panel/performance and maintenance/system/advanced/performance/settings/advanced/virtual memory/change
tick the box that says "system managed size" then set and ok.
or click custom size and enter about twice the value of your installed ram in the min and max boxes.set and ok.