What network is arbitrum on?

I'm curious, can you tell me which network Arbitrum is built on? As a cryptocurrency enthusiast, I'm always looking to stay informed on the latest developments and innovations in the industry. It seems like Arbitrum is gaining a lot of attention lately, and I'd like to understand more about its underlying infrastructure. Is it a Layer 2 solution for Ethereum, or is it built on a completely different blockchain network? Any insights you can provide would be greatly appreciated.