The macula is part of the retina at the back of the eye. It is only about 5mm across but is responsible for all of our central vision, most of our colour vision and the fine detail of what we see.
The macula has a very high concentration of photoreceptor cells which detect light and send signals to the brain, which interprets them as images. The rest of the retina processes our peripheral (side) vision. Macular conditions cause loss of central vision.