function key

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun One of a set of keys on a computer keyboard that execute a function within a given application and are usually numbered 1 through 12.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun computing Any of a set of keys on a personal computer or terminal keyboard used to activate a predefined or programmable function; often labelled F1 to F12, and used in combination with the shift key, alt key and control key