The Nap of the Cloth
If you run your hand gently towards the top of the table the cloth will feel smooth (with the nap); the reverse direction will feel rough (against the nap).
Shots without side
Potting along the top cushion is easier than along the baulk cushion, where the nap may drift the ball away from the cushion with slow shots. The effect is much more pronounced on tables with a heavy cloth. Pots across the table drift slightly towards the top cushion; slow potting of the pink off it’s spot need to be aimed at the lower jaw.
Shots with side
When moving toward the top of the table the cue ball will drift in the same direction as the side but when moving toward the baulk cushion the ball drifts in the opposite direction to the side. So, even with a shaved cloth, if you play with sidespin against the nap the cue ball will turn slightly in the opposite direction that you would want it to. Be very careful to strike plain ball if playing against the nap!
For more information see Nap.