East is most commonly a noun, adjective, or adverb indicating direction or geography.
East is the direction in which the Earth rotates about its axis. Therefore it is the direction from which the sun rises at the equinox. Another consequence is that it is the preferred direction of space launches, because of the saving of delta-v.
East is one of the four cardinal points of the compass, upon which it is considered the opposite of West, and at right angles to North and South.
Moving continuously east is following a circle of latitude, which, except in the case of the equator, is not a great circle.
"The East" also often refers to Eastern countries. When used in this sense, it could, depending on context, refer to the Middle East, Eastern Europe, South Asia, Southeast Asia, East Asia, or even all of Asia. See also: Eastern, Eastern philosophy, Near East, Far East, Levant, Orient
"The East" is also used to refer to the Eastern United States. See also: East Coast
In Mumbai city, East refers to the part of a suburb to the east of the railway line. (See Mumbai suburban railway)
