Altitude or height is defined based on the context in which it is used (aviation, geometry, geographical survey, sport, and more). As a general definition, altitude is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The reference datum also often varies according to the context.
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altitude In general, a term used to describe a topographic eminence.\n(Source: WHIT)
altitude A specific altitude or height above a given level.
altitude The angle between the horizontal and a point at a higher level (in surveying).