A beach is a landscape beside a body of water made up of loose particles. The grains that make up the beach are usually made of rock, such as sand, gravel, shingles, pebbles. Particles can also be biologically derived, such as mollusc shells or coralline algae.

Some beaches have man-made infrastructure, such as lifeguard stations, changing rooms, showers, scaffolding and bars. They may also have hospitality facilities nearby (e.g. resorts, campsites, hotels and restaurants). Wild beaches, also known as undeveloped or undiscovered beaches, are not developed in this way. Wild beaches are valued for their pristine beauty and well preserved nature.

Beaches usually occur in coastal areas, where waves or currents deposit and repair sediments.

Although the term beach is most often associated with beach, beaches can also be found near lakes and rivers.

A beach may mean:

The former will be detailed below; larger geological units will be discussed elsewhere.

There are several distinct parts of the beach that are related to the process of forming and shaping the beach. Most of the parts above the water surface (depending on the tide), and at some point in the tide are more or less positively affected by the waves, are called beach revetments. Revetments are sediments of materials that form the active coastline. The berm has a crest (top) and a face, which is a slope from the crest down to the surface of the water. At the bottom of the face, there may be a trough, further to the sea, with one or more long shore bars: slightly raised, forming an underwater dike, and the waves begin to break first.

Sand deposition may extend inland from the top of the berm, where there may be evidence that one or more older tops (storm beaches) were generated by very large storm waves and exceeded the effects of normal waves. In some cases, waves (even storm waves) stop affecting the materials that make up the beach, and if the particles are small enough (sand size or smaller), the wind will shape the features. If the wind is the force that spreads the grain inland, the sediment behind the beach becomes sand dunes.

These geomorphic features form the so-called beach outline. Due to the variation of wave energy in summer and winter months, the beach profile changes seasonally. In the temperate zone characterized by summer, the sea surface is relatively calm, the interval between wave peaks is longer, and the beach profile in summer is higher. In this season, the gentle action of the waves tends to transport sediment along the beach to the embankment, allowing it to settle and remain as the water recedes. The land breeze further inland formed and enhanced the dunes.

On the contrary, due to the increase of wave energy and the short time interval between wave crests, the beach profile is lower in the storm season (winter in temperate zone). The rapid and continuous rupture of high-energy waves often mobilizes shallow sediments and makes them suspended, because these sediments are easy to be carried along the beach by the long shore water flow, or carried into the sea to form a strip of long shore, especially if the long shore water flows out of the river or flood water. Therefore, removing sediment from beach berms and sand dunes will reduce the beach profile.

In the tropics, the storm season usually occurs in summer, and in winter there is usually calm weather.

If a storm occurs at the same time with an abnormally high tide, or a severe coastal flood is caused at the same time with a strange wave event such as a tidal wave or tsunami, a large amount of material may be eroded out of the coastal plain or sand dunes behind the berm due to the ebb tide. This flow may change the shape of the coastline, enlarge the estuary of the river, and form new deltas at the estuary, which are not strong enough to overcome the coastal movement of sediment.

The boundary between the beach and the dunes is difficult to determine on site. In any important period of time, sediments always exchange between them. The drift line (the highest point of material deposited by waves) is a potential boundary. This is where strong wind sand movement is likely to occur, because normal waves do not wet sand outside the area. However, the drift line is likely to move inland under the storm wave.