It is distinguished from running by the fact that at any time at least one foot has contact with the ground.
For humans walking is the main form of transportation without vehicle or animal. A pedestrian is a walking person, in particular on a road (if available on the sidewalk/path).
Many people walk as a hobby, and in our post-industrial age it is often enjoyed as a form of exercise. The types of walking include bush walking, racewalking, hill walking, volksmarching, and hiking on long distance paths. In some countries walking as a hobby is known as hiking (the typical North American term), rambling (a somewhat dated British expression, but remaining in use because it is enshrined in the title of the important Ramblers' Association), or tramping (the invariable term in New Zealand). More obscure terms for walking include "to go by Marrow-bone stage", "to ride Shank's pony" or "to go by Walker's bus"
The world's largest registration walking event is the International Nijmegen Four Days Marches. The annual Labor Day walk on Mackinac Bridge draws over 60,000 participants. The Chesapeake Bay Bridge walk annually draws over 50,000 participants.
In Britain, the Ramblers' Association is the biggest organisation which looks after the interests of walkers. A registered charity, it has 139,000 members.