Home and Office: Dock It
In addition to a keyboard and pointing device, most likely you'll want to connect at least a few other peripherals to your laptop, such as a printer. But it's a hassle to unplug all those cords when you take your laptop somewhere. That's why you need a port replicator or docking station.
A typical port replicator contains computer ports, such as USB and ethernet networking ports. You connect your peripherals to the port replicator, which in turn is connected to your laptop. Then, when it's time to take your laptop on the road, you just disconnect it from the port replicator, rather than having to unplug all your peripherals.
A docking station does the same thing, but it usually includes slots for expansion cards, CD/DVD drives, and other devices too. In short, a docking station is designed to turn your laptop into something akin to a full-featured desktop computer, while a port replicator simply makes it more convenient to connect peripherals to your laptop.
Generally speaking, third-party port replicators or docking stations may be less expensive than comparable devices from your laptop vendor. For example, a port replicator for Dell Latitude D-Family notebooks often costs about $200, while the Targus USB Mobile Port Replicator with Ethernet lists for $100.
The downside: It's possible to experience compatibility problems with a third-party port replicator or docking station that your computer vendor can't--or won't--solve.
For more details about port replicators and docking stations, see "Mobile Computing: Port Replicators."