A daypack is a small bag you wear on your back, big enough for one day out but not for a long trip. Water, a jacket, lunch, keys — that kind of load. Hikers use the word a lot: a daypack is for a walk that starts and ends the same day, not for sleeping outside. Though actually, many people just say backpack for the same bag; daypack mainly tells you the size and the job. It is casual, shop-and-trail English, more outdoor-catalogue talk than exam-essay talk. Not a suitcase, and not the huge pack travellers drag onto trains.