Is Optimism network the same as Ethereum network?

Could you please clarify for me if the Optimism network and the Ethereum network are interchangeable or fundamentally different? I'm trying to understand the distinction between the two platforms and their respective functionalities within the cryptocurrency and finance landscape. Are they both blockchain-based systems? If not, what are the key differences in their architecture and operation? Also, how do they differ in terms of scalability, security, and the types of applications they support? Thank you for helping me clarify this matter.