One of the very fundamental purposes for using a computer is to send and receive meaningful data (i.e.: files) to and from other users. Sometimes, those users are physically near you, and other times they are a great distance away. When they're near you, there are occasions when it's easier to send/receive those files on a thumb drive or other types of removable media. This is typically the case when you're traveling or otherwise in a location where you're not easily able to both connect to the same network (or any network at all).
Mac OS X has a really useful utility for sending single files (regardless of file size) from one Mac to another.... it's called AirDrop. AirDrop uses a combination of Bluetooth and WiFi to find other nearby AirDrop users and establish a temporary connection with them for purposes of sending files.
Using AirDrop couldn't be easier. Both parties need to open Finder, then click on AirDrop on the left side. After a few seconds of discovering nearby devices, your Finder window will look something like this:
As you can see, there are two other Macs within range that also have AirDrop open in Finder and are available for me to send files to. From here, simply drag and drop the file you want to send onto the icon of the recipient. You are prompted for confirmation that you indeed want to send the file to the other person, as shown here:
Once you click "Send", the the other person receives a prompt to either accept or reject the file:
Once they accept the file, the transfer begins.
AirDrop is very easy to use, but also secure. Both parties have to agree to send and receive the file being transmitted, so you can't sneak a file onto someone else's system without them knowing. AirPlay also uses strong data encryption (TLS), so you can be assured no one else will be able to pick up that file as it's being transmitted. The range for AirDrop is up to 150 feet, line of sight (or less if there there are obstacles). AirDrop is great for sending and receiving files to others in a variety of places and situations like in a coffee shop, on an airplane or even while camping in the middle of absolutely nowhere. Again, no WiFi connection needed. It's completely ad-hoc.
Using AirDrop on older Macs
According to Apple's official marketing materials, AirDrop only works on newer Macs and when WiFi is enabled. However, there's a way to trick your older Mac (and Macs without WiFi) into being able to take advantage of this awesome feature. To do this, open Terminal (Applications > Utilities) and type the following command:
defaults write com.apple.NetworkBrowser BrowseAllInterfaces 1 <enter>
That's it. Your older, WiFi-less Mac can now use AirDrop with newer Macs. If you ever want reverse this change, or for whatever reason completely disable AirDrop (even on newer Macs), use the following command in Terminal:
defaults write com.apple.NetworkBrowser BrowseAllInterfaces 0 <enter>