A close out is a surfing term to describe wave formations that do not allow a tubular ride or smooth ridable transitional and optimum trajectory of hydrodynamic wave action from drop in to either left or right. When a wave closes out, a surfer may drop-in from the wave crest and have nowhere ridable to go without encountering or running into wave action falls blocking his forward momentum or pathway. Normally, the term closing out refers to when the wave sets crest and fall parallel to the shore line. When the wave crests and falls across the whole set line simultaneously, this is referred to as dumping.

Surfing is a surface water sport in which the surfer rides a surfboard on the crest and face of a wave, which is carrying the surfer towards the shore. Waves suitable for surfing are found primarily in the ocean, but are also sometimes found in lakes and rivers, and also in manmade wave pools.

Many variations of the sport may exist in certain areas and the definitions of what constitutes a suitable wave, and craft has expanded over the years. Bodysurfing involves riding the wave without a board, and is considered by some to be the purest form of surfing. Other variations that have existed for centuries include paipo boarding, stand up paddle surfing, and the use of boats or canoes to ride waves. More modern craft that are used include bodyboards, inflatable mats (surfmatting), and foils. As documented in various surfing documentaries (including "Fair Bits") other objects have occasionally been used instead of surfboards, including water skiis, wakeboards, desks, guitars, and doors. When more than one person uses the same craft to ride a wave together, it is known as "tandem" surfing.