This is a video card driver - for an GeForce 6/7/8 series card. Note it was released last year - so you want a more recent version.
If you were asking what is a "driver" - its simply software that tells Windows how to best make use of the graphics ability of your card - without a driver, the card doesn't work - or work as well. Always try to stay fairly up to date on drivers - especially for video cards. However ,sometimes a new version of the driver can make some games not work as well - while others work better. Sometimes its best to live by the rule "If it ain't broke, don't fix it."
Often new drivers for existing cards are released to fix issues with specific games, or to enhance overall performance.
If you have a GeForce 6/7/8 card - you may want to get the most recent drivers. Go here:
http://www.nvidia.com/object/winvist...8.24_whql.html
Note that this does have the WHQL signature - that means that Microsoft has tested it with their operating system and have given it the thumbs up. It doesn't mean its perfect, but it means its stable. Often "beta" drivers are available from various places, and they usually are fine - but if you want to insure stability - use WHQL drivers.