In MacOS 8 and up, this is what you do instead of right clicking to display a context menu. (In case you hadn't heard, all Macs ship by default with one-button mice.)
Click-and-hold is a peculiar case of OS conformity thought up by the Apple developers as Windows 95 began to take over the PC world. Apple proudly held up the one-button mice they had always used as an example of straightforward usability, citing statistics that most Windows users never used their right mouse button or even tried to figure out what it was good for.
Meanwhile, Windows programs continued to add functionality behind the right-click context-sensitive menus. It had its uses in the OS itself, where you could right-click on files or folders to get information, cut and paste, and so forth. But it proved doubly useful when the web browser became the new killer app, and Windows users enjoyed their ability to right-click on links and images to download, launch new browser windows, bookmark links, and so forth. Netscape was probably the first to come up with "click and hold" for their Mac browser as a substitute for right-clicking.
Finally, enough users complained to Apple's OS developers that they established a compromise. The mice would continue to be one-button (or, if you have a more modern Apple Optical Mouse, no-button), but click-and-hold functionality would be built into the operating system in the same manner that Netscape had already built it into their browser. They took it one step further with context menu plug-ins that developers could make that would add new selections to any or all context menus, giving them a chance to thumb their nose at Microsoft once again.*
Of course, most Mac users don't know that "click and hold" is an option to them, the same way most Windows users don't know that the right mouse button is actually good for something. But if you're not the type who regularly visits Apple's or Microsoft's Web site when a new OS release is imminent, you probably don't care.
* For all the good it did them.