One filesystem type that frequently leads to confusion among beginners is swap. It is the equivalent of windows virtual memory, an area on the hard drive that gets used by the processor when it has too many data to remember to fit them all into RAM.
While windows places its virtual memory on the same disk partition as the operating system, Ubuntu and Debian prefer to put it on a partition of its own. This used to be beneficial to overall performance but it is less of an issue nowadays. As the amount of RAM available to the average user has increased tremendously in the past years, which has minimized the risk of RAM overflow, the need for swap space has - particularly on home systems - decreased to the point where some users prefer to use little or even none at all.
One final remark should be made about the NTFS and FAT options that are also available during install. Didn't I say that Ubuntu and Debian do not use windows filesystems? Yes, I did. One should never use these to install the system on. However, Ubuntu and Debian can both read from and write to a Windows system on the same computer (this is know as dual booting: having more than one operating system on the same computer). As Windows is not nearly as curteous, it does not do Ubuntu or Debian the same kind of favour.
Thus a user who wishes to store files in a location that is available to both Windows and Ubuntu/Debian may wish to create an extra partition that has a windows filesystem.
