In this paradox, Zeno argues that an arrow in flight is always at rest. At any given instant the arrow is where it is, occupying a portion of space equal to itself. During the instant it cannot move, for that would require the instant to have parts, and an instant is by definition a minimal and indivisible element of time. If the arrow did move during the instant it would have to be in one place at one part of the instant, and in a different place at another part of the instant. Moreover, for the arrow to move during the instant would require that during the instant it must occupy a space larger than itself, for otherwise it has no room to move. As Bertrand Russel says, "It is never moving, but in some miraculous way the change of position has to occur between the instants, that is to say, not at any time whatever."
Taken from "Zeno's Paradoxes," Edited by Wesley C. Salmon, The Bobbs-Merrill Company Inc, 1970