ELECTIVE
elective
Noun
- Something that is option or that may be elected, especially a course of tertiary study.
Adjective
- Of, or pertaining to voting or elections
- That involves a choice between options; optional or discretionary
- My insurance wouldn't pay for the operation because it was elective surgery.
The above text is a snippet from Wiktionary: elective
and as such is available under the Creative Commons Attribution/Share-Alike License.