They are all good for you, but none of these walks really constitutes hiking. When you go for a walk in the wilderness, in a part of the world that has not been transformed by man, then your walking becomes hiking. When hiking, because your walking is in the wilderness, you have to depend and rely more on yourself your skills and abilities. Hiking gives walking a different feel or flavor. Hiking generally also means walking for longer distances than most of our other walking, but this is not absolutely true.
Many hikes are for only part of day.
A very short hike could be less than a mile on a nature trail by a campground. On the other hand a hike can be a very long walk. Some people hike for days, weeks, or even months at a time. A few people have even hiked for several years at a time. Another nice thing about hiking it s free.