In various programming languages, a kind of variable that is assigned a specific data type but may or may not hold an actual value.
Something that is not compulsory, especially part of an academic course.
Not compulsory; left to personal choice; elective.
Invigorating or life-giving.
Very important.
Containing life; living.
Necessary to continued existence.
Necessary to the continuation of life; being the seat of life; being that on which life depends.
Capable of living; in a state to live; viable.
Relating to the recording of life events.
Relating to, or characteristic of life.