This article deals with the geophysical region in Asia. For geopolitical treatments, see South Asia.
A subcontinent is a large part of a continent. There is no agreement on what constitutes a subcontinent. Generally, however, a subcontinent is split from the rest of a continent by something like a mountain range or by tectonic plates. The phrase the Subcontinent, used on its own in English, commonly means the Indian subcontinent i.e. South Asia.

Geological/geographical subcontinents
In plate tectonics, a small continental plate connected to a larger continental plate can be called a subcontinent. In this sense, the Indian subcontinent on the India Plate and the Arabian subcontinent on the Arabian Plate are recognized. The latter is not commonly called a subcontinent geographically because of lack of a geographical border and a variety in climate. Europe is just a peninsula since it is on the Eurasian Plate.
Geographically, Europe is often described as a subcontinent of Eurasia, a vast landmass in which Europe and Asia are delimited by mountain ranges and inland seas. Similarly, the smallest continent Australasia and the largest island Greenland are sometimes called subcontinents.
North America and South America are sometimes considered two subcontinents of the continent of the Americas (or America) because they are connected by an isthmus. Africa and Eurasia are sometimes considered to form the continent of Africa-Eurasia for the same reason. However, the Americas and Africa-Eurasia are usually called supercontinents, composed of continents.