"HBAR" (ℏ) in physics denotes the reduced Planck constant. This constant is commonly used in quantum mechanics as you can calculate the energy of a photon with the help of this physical constant. Basically, it connects "energy" and "frequency" of light, its wave-properties and its particle-properties.

The discovery of this constant laid the foundation for modern physics and was crucial for the later discoveries of Einstein and Heisenberg. There would be no lasers nor quantum computers without ℏ. I strongly recommend to go down this fascinating rabbit hole. It's intellectually challenging, but highly rewarding.

Now, why would someone call a crypto token $HBAR ? I haven't asked Leemon Baird, the inventor of Hedera Hashgraph, so I have to guess a bit. But after having dived deep into the matter, I recognize that the invention/discovery of the hashgraph has the same transformative power for distributed ledger technologies (DLT) and decentralized consensus mechanisms like the discovery of the Planck constant had for physics. Also, the Planck constant is really cool, so why wouldn't you name a crypto token after it?

But what do I know? I'm just a nerdy woodchuck.

– Chuck Wood