instantaneous velocity

of: a particle (relative to a specific frame of reference)

at: a given time

is: a vector quantity that specifies how fast a body is moving and its direction of motion. [M2.4]

is more specifically: the rate of change of the particle's position at time [M4.1, M5.1, P2.1, P2.2]

is represented: by the vector That is, [M4.1, M5.1, P2.1, P2.2]

has as its SI unit: [M4.1]

can be determined: as the limiting value of average velocity, calculated over shorter and shorter time intervals. [M4.1, P2.1, P2.2]

also can be determined: as the gradient of a position-time graph at time [M4.1, P2.1, P2.2]

usually is known: simply as velocity. [M4.1, P2.1, P2.2]

has: as its magnitude, the speed of the particle. [M2.4, P2.1, P2.2]