Airprint is Apple’s solution for letting iOS 4.2-enabled devices print documents or photos over Wi-Fi to a printer connected to the same LAN as their device without needing to use other software or apps. Airprint is currently supported by a handfull of HP printers, with more expected in the next several months from HP and other vendors.
More info – iOS: AirPrint 101
Printopia: 3rd party, commercial software for the Macintosh that allows wireless printing from Airprint-enabled devices to your Mac’s printers.
Google Cloud Print: the goal of Google Cloud Print is to design a printing experience that enables any app (web, desktop, or mobile) on any device to print to any printer anywhere in the world. NOTE: Google Cloud Print is not yet available.