A beach is a landform along the coast of an ocean, sea, lake, or river. It usually consists of loose particles, which are often composed of rock, such as sand, gravel, shingle, pebbles, or cobblestones. The particles comprising a beach are occasionally biological in origin, such as mollusc shells or coralline algae.

Some beaches have man-made infrastructure, such as lifeguard posts, changing rooms, and showers. They may also have hospitality venues (such as resorts, camps, hotels, and restaurants) nearby. Wild beaches, also known as undeveloped or undiscovered beaches, are not developed in this manner. Wild beaches can be valued for their untouched beauty and preserved nature.

Beaches typically occur in areas along the coast where wave or current action deposits and reworks sediments.

Beaches and recreation
History
Brighton, The Front and the Chain Pier Seen in the Distance, early 19th century.
The development of the beach as a popular leisure resort from the mid-19th century was the first manifestation of what is now the global tourist industry. The first seaside resorts were opened in the 18th century for the aristocracy, who began to frequent the seaside as well as the then fashionable spa towns, for recreation and health. One of the earliest such seaside resorts, was Scarborough in Yorkshire during the 1720s; it had been a fashionable spa town since a stream of acidic water was discovered running from one of the cliffs to the south of the town in the 17th century. The first rolling bathing machines were introduced by 1735.

The opening of the resort in Brighton and its reception of royal patronage from King George IV, extended the seaside as a resort for health and pleasure to the much larger London market, and the beach became a centre for upper-class pleasure and frivolity. This trend was praised and artistically elevated by the new romantic ideal of the picturesque landscape; Jane Austen's unfinished novel Sanditon is an example of that. Later, Queen Victoria's long-standing patronage of the Isle of Wight and Ramsgate in Kent ensured that a seaside residence was considered as a highly fashionable possession for those wealthy enough to afford more than one home.

Seaside resorts for the working class
The extension of this form of leisure to the middle and working class began with the development of the railways in the 1840s, which offered cheap and affordable fares to fast growing resort towns. In particular, the completion of a branch line to the small seaside town Blackpool from Poulton led to a sustained economic and demographic boom. A sudden influx of visitors, arriving by rail, provided the motivation for entrepreneurs to build accommodation and create new attractions, leading to more visitors and a rapid cycle of growth throughout the 1850s and 1860s.

The growth was intensified by the practice among the Lancashire cotton mill owners of closing the factories for a week every year to service and repair machinery. These became known as wakes weeks. Each town's mills would close for a different week, allowing Blackpool to manage a steady and reliable stream of visitors over a prolonged period in the summer. A prominent feature of the resort was the promenade and the pleasure piers, where an eclectic variety of performances vied for the people's attention. In 1863, the North Pier in Blackpool was completed, rapidly becoming a centre of attraction for elite visitors. Central Pier was completed in 1868, with a theatre and a large open-air dance floor.

Many of the popular beach resorts were equipped with bathing machines because even the all-covering beachwear of the period was considered immodest. By the end of the century the English coastline had over 100 large resort towns, some with populations exceeding 50,000.

Beach wildlife
A beach is an unstable environment that exposes plants and animals to changeable and potentially harsh conditions. Some animals burrow into the sand and feed on material deposited by the waves. Crabs, insects and shorebirds feed on these beach dwellers. The endangered Piping Plover and some tern species rely on beaches for nesting. Sea turtles also bury their eggs in ocean beaches. Seagrasses and other beach plants grow on undisturbed areas of the beach and dunes.

Ocean beaches are habitats with organisms adapted to salt spray, tidal overwash, and shifting sands. Some of these organisms are found only on beaches. Examples of these beach organisms in the southeast US include plants like sea oats, sea rocket, beach elder, beach morning glory (Ipomoea pes-caprae), and beach peanut, and animals such as mole crabs (Hippoidea), coquina clams (Donax), ghost crabs, and white beach tiger beetles.

The coast is defined as the part of the land adjoining or near the ocean. A coastline is properly, a line on a map indicating the disposition of a coast but the word is often used to refer to the coast itself. The adjective, coastal describes something as being on, near to or associated with a coast.

Coast is a specific term, and is applied to that part of an island or continent that borders an ocean or its saltwater tributaries. A pelagic coast refers to a coast which fronts the open ocean, as opposed to a more sheltered coast in a gulf or bay. A shore on the other hand, can refer to parts of the land which adjoin any large body of water, including oceans (sea shore) and lakes (lake shore). Similarly, the somewhat related term bank refers to the land alongside or sloping down to a river (river bank) or of a body of water smaller than a lake. Bank is also used in some parts of the world to refer to an artificial ridge of earth intended to retain the water of a river or pond. In other places this may be called a levee.

While many scientific experts might agree on a common definition of the term "coast", the delineation of the inland extents of a coast differ according to jurisdiction, with many scientific and government authorities in various countries differing for economic and social policy reasons. This is usually because defining lands as part of a coast may be seen to have environmental implications which would prevent development or attach regulations to their use.