Implied texture refers to any texture that is seen by the eye but that does not really exist. Consider this sculpture. It has both actual texture and implied texture. The actual texture is the marble from which it is carved (the medium). The implied texture can be seen in the folds of the rumpled clothing, the smoothness of pliable skin, and the softness of the hair. Note that both the skull and the skin are smooth and yet the implied textures suggest a clear difference between the soft and hard textures that are implied.
This technique is even more pronounced in works that are in two dimensions. This painting by Caravaggio features implied textures of rumpled clothing, soft and bristly hair, smooth pliable skin, and a sharp sword. And yet, all we would feel touching it would be paint and canvas.