Optionality is a concept that is used in many different contexts. Facultative, VOLUNTARY, ELECTIVE, and EXTRA are all terms that refer to something being optional. Facultative, with 11 letters, means that something is allowed but not required. VOLUNTARY, with 9 letters, means that something is done of one's own free will. ELECTIVE, with 8 letters, means that something is chosen from a range of possibilities. Finally, EXTRA, with 5 letters, means that something is additional or beyond what is necessary. All of these terms refer to the concept of something being optional.