The term ambisextrous is a slang word used to describe sexual flexibility. It is a playful version of the word ambidextrous, which describes someone who has the ability to use both their right and left hand with ease. The term ambisextrous gained popularity somewhere between 1965 and 1970.
Similar to how people who are ambidextrous can write just as well with their left hand as with their right, an ambisextrous person may be equally capable of falling in love with a man or a woman, or being versatile in their sexual practices.