n. a directed line from the origin of a coordinate system to a point in space, regarded as variable and sweeping out a curve. If it is the vector OP, where the coordinates of P are (x, f(x)), it can also be represented as <x, f(x)>, that is, as the n-tuple of its components in the directions of, or projections onto, the coordinate axes. See also position vector. OP is the radius vector of the curve described by P.