Shibarium, released in August 2023, is Shiba Inu’s Ethereum Layer 2 Blockchain.
“Shibarium was presented as one of the primary goals of the Shiba Inu experiment as it, theoretically, would reduce transaction fees for those involved in the Shiba ecosystem.”
In order to interact with projects on the Shibarium chain you need to use the Shibarium Token Bridge to cross over from the Ethereum blockchain.