Moiré pattern occurs when a scene or an object that is being photographed contains repetitive details (such as lines, dots, etc) that exceed the sensor resolution. As a result, the camera produces a strange-looking wavy pattern as seen below:
(Image courtesy of photo.net)
See how noticeable the moiré pattern is on the jacket? That’s moiré for you, at its worst. Moiré is almost never seen in nature, but is very common in everyday objects and items around us – you might see it in all kinds of fabric, straight hair, architecture, etc. You might have even seen it on your television. In photography, moiré happens mostly because of the way light reaches the sensor and how the sensor interprets the light through the bayer interpolation filter.
While there are methods to effectively reduce moiré, there is no easy way to completely remove it in post-processing software. Lightroom 4 will ship with a moiré reduction tool and Nikon will also ship its next version of Capture NX with built-in moiré reduction functionality, but neither one will be able to fully get rid of the worst moiré pattern occurrences.
See “How to Avoid Moiré“