How Do I Re-install Terminal Application?

You should be able to copy the application back by using the original install media that came with your computer.

I've noticed that Apple re-organizes the layout of the original factory install media from time to time. For example, on my MacBook Pro, I can insert 'Disk 1' and once the DVD mounts you see names like 'Install Mac OS X and Bundled Software', but if you scroll the Finder window down a bit, you'll see there's an Applications folder. You should be able to drag the Terminal.app from the Applications folder on your DVD to the Applications folder on your internal hard drive. Your install media might locate things in different folders depending on the version, but you should be able to find it if you snoop around.

Restoring Lost OS X Files

If you erase or otherwise "lose" an OS X system application or utility (such as Mail or Disk Utility, for example) you can restore them without having to reinstall OS X.

Download the shareware utility Pacifist. Read the documentation. Use Pacifist to extract a fresh copy of the missing application from the file archives on your OS X Installer disc. The file archives are usually found on the installer disc in the /System/Installations/ folder.

After restoring the application you need to reinstall the OS X Combo Updater for the version of OS X you currently have installed. This assures the new copy of the application is updated to the current version.

Lastly, it's a good idea to repair permissions.