The Terminal or Terminal.app is an industry standard command shell which gives you full access to the UNIX underpinnings of Mac OS X. You can use standard UNIX commands, scripting languages and tools in the Terminal.
Included with the terminal are a number of short cuts you might not be used to in other UNIX terminals. You can cut and paste commands, drag and drop files into the Terminal. Finally, you can customize the Terminal to your hearts content, adding fonts, background colors.