The term adult describes any mature organism, but normally it refers to a human: one that is no longer a child / minor and is now either a man or a woman. Coming of age is the event of becoming an adult, i.e. of entering adulthood.

"Adult" also means "not considered suitable for children", in particular as a euphemism for being related to sexual behaviour, such as adult entertainment, adult video, adult magazine, adult bookstore. However, adult education simply means education for adults, not particularly sex education.