"Bricking" - attempting to update the firmware of your phone, something goes wrong (usually the user touches the phone and knocks the cable loose or something stupid, there's a thread debating this, though) and the update doesn't go through, in which case the phone only technically has half of the firmware, and won't turn on, thus being reduced to a "brick"
"Firmware" - the version of the operating system of your phone. Your phone runs Symbian S60v3 like your computer runs Windows, but the firmware is 3.065.9.4 (or whatever the number is) like your computer is XP SP2 (only firmware is phone-specific, i.e. you can't put N91 firmware on an E61).
"Hard Reset" - completely resets the phone to the exact condition it was shipped from the factory with.
"Soft Reset" - simply erasing all the user-added data
Hope that helps.
