Crown is a period 12 oscillator that was found by Noam Elkies in January 1995. Alternatively, it may refer just to the 10-cell piece at the top of the oscillator in generation 10 (shown below in green) that is hassled by 2 caterers and the heavyweight emulator.
It is used in the pi orbital and p156 Hans Leo hassler.
By replacing the caterers with extensible p3 oscillator, an extensible crown can be made.
Generation 10 reveals a piece that by itself is sometimes referred to as the crown