Optional
Voluntary, Arbitrary
の adjective
My idea of duty is that you don't really have to do it. It's optional, you know?
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.
フォローは任意です。
You can follow me on a voluntary basis.
任意の八ケタの数字を選んでください。
Please choose any 8-digit number.
名前と住所は法律で答えなくてはいけないと決まっているものですか？それとも任意ですか？
Do I legally have to tell you my name and address, or is it optional?