A Headland is an area of land adjacent to water on three sides. A bay is the reverse, an area of water bordering land on three sides. Headlands and bays are usually, but not always, found together on the same stretch of coastline. Headlands and bays form on concordant coastlines, where bands of rock of alternating resistance run perpendicular to the coast. Bays form where weak (less resistant) rocks (such as sands and clays) are eroded, leaving bands of stronger (more resistant) rocks (such as chalk, limestone, granite) forming a headland, or peninsula. Wave refraction occurs on headlands concentrating wave energy on them so many other landforms, such as caves, natural archs and stacks, form on headlands. Wave refraction disperses wave energy through the bay, and along with the sheltering effect of the headlands this protects bays from storms. This effect means that the waves reaching the shore in a bay are usually constructive waves, and because of this most bays feature a beach. A bay may be only metres accros, or it could be hundreds of kilometres accros.
Headlands and bays may also form in lakes.
Sometimes bays may also form where movements of the earth's crust (tectonics) bring areas of land together, or move them apart. Usually these bays are referred to as seas or gulfs and not bays.
Headlands, particularly large headlands, may also be called peninsulas, or where they dramatically affect the ocean currents they are called capes.
"Capes and bays geography" is a derogatory term for the approach to teaching geography that requires students to rote learn the names of large number of geographical features rather than taking a more theoretically driven approach.
List of some well-known bays