FLV files are basically Flash videos which require a special player. FLV files are mostly available for downloads from popular video sites such as YouTube, Megavideo, Google Videos etc. If you have downloaded a FLV file but cannot play it on your PC, you will require to download additional softwares to be able to view it.
Wimpy Desktop FLV Player is a free software that will allow you to play FLV files you have downloaded to your desktop.
The player does not require any installation, so you can use it from a portable drive too. Wimpy desktop FLV Player is a freeware and is available for both Windows and Mac OSX.