Is Ethereum and Arbitrum the same thing?

Is Ethereum and Arbitrum interchangeable concepts, or are they distinct entities within the realm of cryptocurrency and blockchain technology? Could it be that they share similarities in functionality or purpose, yet maintain unique characteristics that set them apart? Alternatively, are they completely unrelated, serving different roles in the digital currency ecosystem? I'm curious to understand the relationship, if any, between these two terms and how they fit into the broader context of crypto finance.