If you're always carefree and relaxed, your friends might describe you as easygoing. Easygoing people probably get invited on camping trips more often than uptight, tense people do.
If your school has an easygoing dress code policy, it's probably fine if you wear a clown costume or high-heeled, glittery shoes to school. If your Spanish teacher isn't quite so easygoing, though, he may ask you to remove your red nose and wig before class starts. This adjective, which sounds fairly modern, has been around since the 1640s.