vector vec·tor (věk'tər)
An organism, such as a mosquito or tick, that carries disease-causing microorganisms from one host to another.
A bacteriophage, a plasmid, or another agent that transfers genetic material from one location to another.
A quantity, such as velocity, completely specified by a magnitude and a direction.
In physics and mathematics, any quantity with both a magnitude and a direction. For example, velocity is a vector because it describes both how fast something is moving and in what direction it is moving. Because velocity is a vector, other quantities in which velocity is a factor, such as acceleration and momentum, are vectors also.