Answer
Rayleigh–Taylor instability is a hydrodynamic instability that occurs when a fluid with a higher density is placed above a fluid with a lower density. This instability can lead to the formation of Rayleigh–Taylor fingers, which are long, thin columns of the denser fluid that extend into the less dense fluid. Rayleigh–Taylor instability is named after Lord Rayleigh and G. I. Taylor, who first described the phenomenon in 1920.