Not compulsory; left to personal choice; elective.

Something that is not compulsory, especially part of an academic course.

In an optional manner. Not mandatorily.

(finance, business) The value of additional optional investment opportunities available only after having made an initial investment. / Quality or state in which choice or discretion is allowed.

plural of optionality

plural of optional

simple past tense and past participle of optionalize

present participle of optionalize

Third-person singular simple present indicative form of optionalize

To make optional; to add as an option, permit to be optionally omitted, or provide various options for implementing.