Read the dictionary definition of facultative. All definitions for this word.
1. not compulsory
1. elective surgery
2. an elective course of study
2. granting a privilege or permission or power to do or not do something
1. a facultative enactment
3. able to exist under more than one set of conditions
1. a facultative parasite can exist as a parasite or a saprophyte
4. of or relating to the mental faculties