In optical systems, a speckle pattern is a field-intensity pattern produced by the mutual interference of partially coherent beams that are subject to minute temporal and spatial fluctuations.

Note: In a multimode fiber, a speckle pattern results from a superposition of mode field patterns. If the relative modal group velocities change with time, the speckle pattern will also change with time. If differential mode attenuation occurs, modal noise results.

Source: from Federal Standard 1037C and from MIL-STD-188

A speckle pattern of antinuclear antibody (ANA) is characteristic of the disease lupus erythematosus.