elective
e-lec-tive
adjective
Relating to something chosen by election or available as an option, not compulsory.
"Students can pick an elective module."
noun
An optional academic course or subject that a student can choose.
"He took history as an elective."
Thesaurus
Synonyms: nonappointive, electoral, elected, optional, facultative, elective course
Antonyms: appointed, appointive