Cow stomach (beef tripe) in meat market (Laos)
Actually this is from a water buffalo. What you see is the inside of one of the four stomachs of the cow. It has been cleaned and put inside-out. It has a fractal honeycomb structure (reticulum).
Tripe meat is made of the animal stomach and parts of its intestine.
Water buffalo have a black stomach (and black skin), while most cows have a white stomach, so generally tripe meat is white.
Some people claim to be repulsed at the sight of objects with small holes, like this photo. The condition is called Trypophobia. For more info, read en.wikipedia.org/wiki/Trypophobia.