Texture is perceived surface quality. There are two types of texture: tactile and implied. Tactile texture (real texture) is what we are most familiar with. It is the way the surface of an object actually feels. Examples of this include sandpaper, cotton balls, tree bark, animal fur, etc. Implied texture is the way the surface on an object looks like it feels. The texture may look rough, fizzy, gritty, but cannot actually be felt. This type of texture is commonly used by artists when drawing or painting.
I liked this photo because it depicts a few different textures from the roughness (and smoothness) of some of the river rocks and also shows the prickly leaves of the weeds growing through the rocks.