Partitions are divisions of your hard drive. X86 BIOS recognizes four primary partitions. Operating systems have ways of subdividing those further. Linux can make at least 16 "partitions" on your hard drive. The terminology can be confusing but they all refer to the same thing.
Linux treats each partition, primary or logical, as a device and you can find them in your /dev directory. "Normal" IDE hard drives are refered to as:
/dev/hda1
Where "hd" tells you the device is IDE hard drive, "a" tells you it's the first device and "1" is the first partition. It does not take much imagination to guese that /dev/hdb1 refers to the first partition on the second IDE hard drive.