What is the difference between Filesystem and "Extended Partition" in Disks?

An Extended Partition is an artifact of MBR 'legacy' disk partitioning, as the MBR system only allows a maximum of four (4) partitions. To have more than four partitions, an Extended Partition is used to hold multiple Logical Partitions.

This was obsoleted by the GPT Partition Table, which removed the cap of four (4) partitions on a disk, but there are still plenty of folks out there with the MBR 'legacy' partition tables, as Windows 7 and earlier versions of Windows defaulted to the MBR 'legacy' partition tables. I suspect that's what I see in your picture above.

BTW, Partition 1 of that drive is a Windows Recovery Partition. It is a Primary Partition, just like the NTFS partition (Partition 2).

For more on filesystems, see this article.

An extended partition is a partition that can be further divided to create additional partitions.

Basically, the extended partition allows you to have more partitions on a physical drive than you could otherwise have.

Here is an example of a disk with five partitions and a link to a definition of an extended partition.

http://www.info.org/extended_partition.html

$ df -a /dev/sda*
Filesystem     1K-blocks      Used Available Use% Mounted on
udev             3910716         4   3910712   1% /dev
/dev/sda1      493235028  36226812 431930208   8% /
udev             3910716         4   3910712   1% /dev
/dev/sda5      151058636 107940272  35421980  76% /media/stephen/Hitachi72101Ptn5
udev             3910716         4   3910712   1% /dev
/dev/sda7      157554484    609108 148918960   1% /media/stephen/Hitachi72101Ptn7
/dev/sda8      151058636     60884 143301368   1% /media/stephen/Hitachi72101Ptn8