optional

Meanings

1. 1
   adj

   Not compulsory; left to personal choice; elective.

   On that beach clothing is entirely optional.

2. 2
   noun

   In various programming languages, a kind of variable that is assigned a specific data type but may or may not hold an actual value.

   In functional languages, there is a data type called the option type, also called the maybe type. Its purpose is to encapsulate a value, which is returned from a function. […] In Java 8, the Optional class has been added to serve as an option type.

3. 3
   adj

   possible but not necessary

4. 4
   noun

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

Etymology

From option + -al.