This is the most common form of IP packet. A unicast packet is sent from one system to a single destination. The header of the
IP packet contains the source address (so the remote system can respond) and the
destination address. Routers will look at the packet and then hand it off to the next closest
router; this process continues untill the packet times out (too many hops) or until it reaches it's destination.
Unicast is designed for situations where the content being sent to each client is different, but faces some major performance issue when numerous clients request the same content (such as streaming video) as the server must send the data once to each client.
See also:
IP Multicast,
IP Broadcast