The Airport is the brand name for the wireless ethernet equipment used by Apple Macintosh computers (first found in the iBook but now every shipping Macintosh is "airport ready").
Airport uses the IEEE 802.11 Direct Sequence Spread Spectrum (DSSS) standard to broadcast and receive Ethernet packets. This means Airport is compatible with any computing using the same standard including Wintel machines using Lucent Orinoco/WaveLAN cards.
Computers equipped with Airport cards need to connect to either a Airport Basestation or another Airport equipped computer running the "Software Basestation" software. The range of the Airport card does vary on conditions but in practical tests I've managed to get a good signal and connection speeds at around 75'-100' from my G4 running Software Basestation.
Oddly enough some Airport Terminals are being equipped with Airport/IEEE802.11 basestations. I guess this means the Airports are Airport ready. Austin International Airport is just one of many airports with Airports installed.
Computer Conferences are also using Airport/IEEE802.11 basestations to provide internet access to their attendees. I first encountered Airport on this scale at the WWDC conference in San Jose in May 2000. Eighteen Airport Basestations were spread throughout San Jose Conference Centre (glued upside down to the ceiling) allowing everyone with an Airport equipped laptop to go online. It was a most effective demonstration of the Airport technology.