na-adjective
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).
この科目は選択的なので、興味があれば受講してください。
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.
選択 is the noun 'choice' or 'selection'; 選択的 is the adjectival form meaning 'involving choice' or 'selective'.
From 選択 (せんたく, 'choice') + 的 (てき, '-ive'). The suffix 的 forms adjectival nouns from nouns, often corresponding to English '-ive' or '-al'.