AirPort is Apple's name for WiFi wireless networking.
The original AirPort was 802.11b 11Mbps wireless.
AirPort Extreme is 802.11g 54Mbps wireless. It is backwards-compatible with the original.
As of today, all PowerBooks include AirPort Extreme cards standard. Lots of public places offer wireless internet access (some free, some for money), and it's really handy at home. Apple's base stations ("access points") are pricey but nice, and really easy to set up. Third-party ones aren't quite as intuitive, but cost as little as 1/4 as much as Apple's.
tooki