Up may refer to any of the following:
1. Up is a term used to describe a computer or software program is functional and ready for use. For example, the Computer Hope website is up since you can read this page. If the site was down, you would get an error when trying to load this page.
2. One of four arrow keys that moves the cursor in an upward direction. In the picture there are four arrow keys, the top key is the up arrow key. If you were using the WASD keys for your arrow keys the "W" key would be used as the up arrow key.