Shimmering false patterns and colors that appear when a fine, regular pattern in the subject interferes with the regular grid of the sensor. It is a form of random noise: it depends on the subject, so the camera cannot map it out in advance.
Noise that depends on the subject as much as on the sensor. It arises where fine detail falls awkwardly across pixel boundaries and through the demosaicing arithmetic: a line half in one pixel and half in the next. Because it changes with every scene, the camera cannot mask it out in advance the way it removes hot pixels. Moiré is its most dramatic form.
Fujifilm's alternative to the Bayer array. It keeps the green majority but lays the filters out in a larger, less regular pattern, and the irregularity is the point: with no strict grid for the subject's own patterns to drum against, fine weaves and textures cause far less moiré.