Ephebophilia is when an adult is mostly or only sexually attracted to people in their mid-to-late teenage years, generally those in the age range 15-19. An adult with this attraction is called an "ephebophile". Ephebophilia is not just the sexual attraction to teenaged partners, but is when an adult prefers such sexual partners.
Specific words are used by scientists for chronophilias (which is when people are mostly or only sexually attracted to specific age groups). Along with ephebophilia, another example is hebephilia, which means that a person is mostly or only sexually attracted to younger, pubescent people. The word pedophilia means that a person is mostly or only sexually attracted to children who have not reached puberty. However, the term pedophilia is commonly, but incorrectly, used to refer to any sexual interest in any person under the age of 18, regardless of whether they are post-pubescent.