I've talked about the so-called "Gap Year" before. According to aptly named PlanetGapYear.com, a Gap Year is "a period of time when students take a break from formal education to travel, volunteer, study, intern, or work. A gap year is also referred to as a deferred year, year out, year off, time out, time off. A gap year experience can last for several weeks, a semester, or up to a year or more. Typically a gap year is taken between high school graduation and starting college, during college, or between college and starting graduate school or a career."
In my work as an independent college admissions counselor, I encounter a year-gapper now and then. I enjoy working with them because they all have seemed to have a mature and considered outlook on their higher education needs. There seem to be two main motivations for their desire to take a Gap Year: (1) They need to take a break from that long, unbroken chain of years from K through 12, or (2) they haven't yet figured out what they want to do with their lives, so a year of exploring their "hearts" might just bring things into focus. There are no doubt other reasons that high school seniors stop out for a year before college, but these two reasons seem to be the most prevalent, at least in my experience.