Is arbitrum like Ethereum?

Could you please elaborate on the similarities and differences between Arbitrum and Ethereum? I'm curious to know if Arbitrum operates in a similar manner to Ethereum, given their respective roles in the cryptocurrency ecosystem. Could you compare their functionalities, scalability, and potential use cases? Additionally, how does Arbitrum's approach to scalability differ from Ethereum's? Is Arbitrum considered a competitor or a complementary solution to Ethereum? I'm eager to gain a deeper understanding of their relationship and how they fit into the broader cryptocurrency landscape.