From Longman Dictionary of Contemporary Englishoptionalop‧tion‧al /ˈɒpʃənəl $ ˈɑːp-/ ●●○ AWL adjective MUSTif something is optional, you do not have to do it or use it, but you can choose to if you want to OPP compulsory three optional courses The other excursions are optional.optional extra British English Leather seats are an optional extra.RegisterIn everyday English, people often say that you don’t have to do something rather than say it is optional: Ties are optional. → You don’t have to wear a tie.
Examples from the Corpus
optional• Attendance at the meeting is optional.• You don't have to do French - it's optional.• At the same time optional accessories, such as cornices, light pelmets and plinths, could also be changed.• If they wish, students can do an optional dissertation, and pick up word-processing and other computer skills.• The holiday price includes entertainment in the evenings, and there are optional excursions on offer every day.• General Studies is optional for sixth-form students.• All freshmen who attend optional orientation sessions receive information on date rape.optional extra• Most of the systems offer optional extras.• No, sorry, massager is an optional extra.• Reading is not an optional extra.• This can be fitted with push release toggle as an optional extra.• Return flight back to U.K. or optional extra day in Stockholm, for sightseeing or a visit to a local woodworking group.• Etiquette and good manners are not a middle-class pastime or an optional extra for nice people.• An optional extra is a rainfall monitor.• Atheism for Marxism is not an optional extra or a mere facet but the very essence of it.From Longman Business Dictionaryoptionalop‧tion‧al /ˈɒpʃənəlˈɑːp-/ adjective if something is optional, you can choose whether or not you have it, do it, or use itYou can have a 17-inch monitor as an optional extra (=something that is additional to or better than the basic type).The use of a password to access the system is optional. → compare standard2 