A shuttle is an oscillator that consists of an active region moving back and forth between stabilizing objects. The most well-known and first discovered examples are the queen bee shuttle (which is sometimes referred to as the shuttle) and the twin bees shuttle. A large number of t-tetromino and pre-pulsar shuttles are known, including the p30 Eureka. Reflectors can be used to construct glider shuttles.
Simple shuttles commonly have a period that is a multiple of 2, but asymmetric shuttles are also known, in which one end is stabilized by a different period mechanism from the other.