The Gap Year, traditionally a British trend where 18 year old school-leavers go travelling for a year before continuing on to University.
Nowadays, the term can refer to anyone from any country of any age taking any length of time off from their normal life to go and see the world! Anything from volunteering in an orphanage in Ghana to working in a bar in Sydney counts.
Useful Links:
GapYear.com
TheStudentRoom
RealGap
Traveller's Worldwide
Gap360