Riding, say is a term used to describe the activity of riding an animal or vehicle. It is a form of transportation that has been used for centuries and is still popular today. ATOP is the four letter solution to this crossword clue, which can be interpreted as being on top of something, such as a horse or a bike. This phrase is often used to describe the act of riding, as one is literally ATOP the animal or vehicle they are using to get from one place to another.