Air-to-air missiles are broadly put in two groups. Those designed to engage opposing aircraft at ranges of less than 30km are known as short-range or “within visual range” missiles (SRAAMs or WVRAAMs) and are sometimes called “dogfight” missiles because they emphasize agility rather than range. Most use infrared guidance and are called heat-seeking missiles. In contrast, medium- or long-range missiles (MRAAMs or LRAAMs), which both fall under the category of beyond visual range missiles (BVRAAMs), tend to rely upon radar guidance, of which there are many forms. Some modern ones use inertial guidance and/or "mid-course updates" to get the missile close enough to use an active homing sensor.