Apple AirPrint allows wireless printing from iPad / iPhone / iPod devices running modern versions of the Apple iOS operating system. This Apple technology is just enabled on a range of Hewlett-Packard printers, but with some CUPS modifications, it's possible to make your Linux system look like an AirPrint-compatible printer. What this means is that from your portable Apple iOS device you can send print jobs to your Linux system that in turn will print to your attached printer. Alternatively, you can create a "fake" printer to dump the AirPrint jobs to a PostScript file.
AirPrint support on Linux isn't an original Ubuntu innovation, but this Apple technology was made to work under CUPS on Linux last year by a developer as mentioned on this blog posting. The new CUPS packages that have been updated to the Ubuntu Natty and Ubuntu Oneiric packages are based upon this work.
Assuming your printer is set to be shared via CUPS and you're running the latest packages, from your Apple device you can now send print jobs via WLAN. Additional details can be found in this ubuntu-devel posting.