A thing which is autotelic is described as "having a purpose in and not apart from itself".
The word comes from the Greek αὐτοτελής autotelēs from αὐτός autos, "self" and τέλος telos, "goal".
Mihaly Csikszentmihalyi describes people who are internally driven, and as such may exhibit a sense of purpose and curiosity, as autotelic. This determination is an exclusive difference from being externally driven, where things such as comfort, money, power, or fame are the motivating force.
"An autotelic person needs few material possessions and little entertainment, comfort, power, or fame because so much of what he or she does is already rewarding. Because such persons experience flow in work, in family life, when interacting with people, when eating, even when alone with nothing to do, they are less dependent on the external rewards that keep others motivated to go on with a life composed of routines. They are more autonomous and independent because they cannot be as easily manipulated with threats or rewards from the outside. At the same time, they are more involved with everything around them because they are fully immersed in the current of life." 
In a sense the action itself is an expression of their happiness, and not a desire to achieve or have happiness.
- Ophelimity, another term for whether a thing has useful contingency (purpose through specific utility) or is an end with purpose unto itself.
- End in itself
- Intrinsic motivation
- The dictionary definition of autotelic at Wiktionary