The Heaviside layer, sometimes called the Kennelly–Heaviside layer, named after Arthur E. Kennelly and Oliver Heaviside, is a layer of ionised gas occurring roughly between 90km and 150 km (56 and 93 mi) above the ground — one of several layers in the Earth's ionosphere.

What does the Heaviside Layer represent?

In the context of Cats, the Heaviside Layer is essentially Heaven, or the next step of existence that leads to reincarnation. It's where the chosen Jellicle cat is sent before they can become the cat they have always wanted to be reborn into.

Why are the cats mean to Grizabella?

Grizabella is a lonely old cat who has been shunned by the other Jellicle Cats, possibly because she is implied to be a sex worker, which is bad praxis on the part of the Jellicles. Grizabella is probably the most coveted and well-known role in the play, and is usually played by a celebrity or respected Broadway dame.