Low-pass filter (LPF)
From The Glossary of Digital Photography
Also called anti-aliasing filter. As the name implies, a filter that passes lower frequencies and cuts off higher frequencies. An example would be the filter located in front of the image sensor in to reduce moire or aliasing patterns. The low-pass filter has a tendency to reduce the sharpness of the image. It is usually designed to remove infrared light (IR). See anti-aliasing; infrared
