A person who seeks sexual partners, without care, or restrictions. To seek and engage in indiscriminate sex, with any willing partner. To engage in a sexual affair or relationship, outside of their existing relationship.
Mostly used in jest, as in reference to one who sleeps around a lot.
Also used to jokingly refer to someone who always looking for sex, as one who just can't get enough of a good thing.
Can be used in a negative manner, implication being they are never satisfied with what they get, sexually.