What is a swap partition and how do i creat it on installing linux?

I am trying to install Linux xp by fedora redhat and it is telling me that I need to specify a swap partition.

Off of a 160GB HD I have partitioned 40GB for the Linux as a secondary OS I have created a (/) and a (/home) for it now its telling me to specify a swap partition how do i do this?What is a swap partition and how do i creat it on installing linux?
The swap partition is just like virtual memory(Paging Files)in XP or some space which is needed twice the size of physical memory or RAM. this space is used by linux to store files when your RAM is loaded fully. you can create this partition during installation of linux by simply selecting the space on your hard disk and select /swap from the drop down box.