A crop variety is tolerant if the pest can live on the plant, but the plant is not seriously affected by the pest.
For example most rice varieties are tolerant against leaf feeders. If leaf damage is not too severe (even up to 50% leaf damage in a young plant), the plants compensate by producing extra leaves or tillers.
Note that a tolerant variety in not the same as a resistant variety. Compare tolerance and resistance in the picture below.
