Apple terminology for
symbolic link or
shortcut. A small placeholder file that
represents its
target in a different location.
For example, when I create a piece of artwork that my art director needs to review before I send it on to the build team, I have to log on to the projects server, find the folder for this project and the sub-folder of my work and the sub-sub-folder for this week, and copy my file there. Instead, I keep an alias of that sub-sub-folder in the same folder on my machine as my work, and drag the new artwork onto that alias. If the network connection is already established, the file gets copied to the right place without all the extra navigation. If the server is not mounted, double-clicking or dragging to the alias makes the connection automatically (on Macs, anyway).
Aliases are also an underused solution to the "User Keeps Everything They Ever Use On Their Desktop" problem.