hda3 ext3 8.39gigs 327.53 megs 8.07 gigs
It is either a pre-existing partition that Mepis recognizes, or you created it during the process of installing Mepis.
Cat /etc/fstab to see if it's listed. It will show you the device /dev/hda3 and the mount point. Cd to the mount point and list the contents (or use your GUI filemanager to inspect the contents of the mount point).
What kind of files do you see?