What the programmer wants to do is take a current position for an object and form a smooth path to where the object is supposed to be.
Several techniques are available.
As its name implies, this method involves only moving a player to a new point when a data-packet arrives. This method is by far the worst because unless a remote player is absolutely still, his onscreen representation is completely erroneous. The only way to make players move smoothly is to send one packet for every game frame. This method involves creating a straight-line path to the next position. In terms of physics, this means that the velocity of an object is used to decide where it should next appear.