According to Oxford English Dictionary, the term "subcontinent" signifies a "subdivision of a continent which has a distinct geographical, political, or cultural identity" and also a "large land mass somewhat smaller than a continent". It is first attested in 1845 to refer to the North and South Americas, before they were regarded as separate continents. Its use to refer to the Indian subcontinent is seen from the early twentieth century. It was especially convenient for referring to the region comprising both British India and the princely states under British Paramountcy.
The term Indian subcontinent also has a geological significance. Similar to various continents, it was a part of the supercontinent of Gondwana. A series of tectonic splits caused formation of various basins, each drifting in various directions. The geological region called "Greater India" once included Madagascar, Seychelles, Antarctica and Austrolasia along with the Indian subcontinent basin. As a geological term, Indian subcontinent has meant that region formed from the collision of the Indian basin with Eurasia nearly 55 million years ago, towards the end of Paleocene.
The geographical region has historically simply been known as "India" (in antiquity referring to the Indus Valley region, not the entire subcontinent). Other related terms are Greater India and South Asia.
And the terms "Indian subcontinent" and "South Asia" are sometimes used interchangeably. There is no globally accepted definition on which countries are a part of South Asia or the Indian subcontinent.
The less common term "South Asian subcontinent" has seen occasional use since the 1970s.