selective; optional; alternative
Describes something that involves choice or is not mandatory. Often used in technical or formal contexts, such as 選択的夫婦別姓 (selective separate surnames for married couples).
This subject is optional, so please take it if you are interested.
選択的夫婦別姓制度の導入が議論されている。
The introduction of a selective separate-surname system for married couples is being discussed.
selective serotonin reuptake inhibitor; SSRI