AirDrop is a new feature Apple will be including in Mac OS X Lion that will allow you to wirelessly transfer files to anyone around you as long as they're also running OS X Lion with AirDrop. Here's a quick description of how AirDrop will work:
With AirDrop in Mac OS X Lion, you can send files to anyone around you — wirelessly. AirDrop doesn’t require setup or special settings. Just click the AirDrop icon in the Finder sidebar, and your Mac automatically discovers other people nearby who are using AirDrop. You’ll even see contact photos for those who are already in your Address Book. To share a file, simply drag it to someone’s name. Once accepted, the file transfers directly to the person’s Downloads folder. When you’re done with AirDrop, close the Finder and your Mac is no longer visible to others.
If that sounds to you like AirPlay or AirPrint for files, well it does to us as well. However Apple hasn't mentioned anything about extending AirDrop to iOS (yet). In theory this would work great for transferring photos, documents, and even media from your Mac to an iPhone or iPad.