Is dYdX an Ethereum?

Could you please clarify for me: is dYdX considered to be an instance of Ethereum? I've heard some discussions about it being related to the Ethereum blockchain, but I'm not entirely sure about the specifics. Could you explain the relationship between dYdX and Ethereum, if any? Is dYdX built on top of Ethereum or does it operate independently? Also, what are the key differences between dYdX and other projects within the Ethereum ecosystem? Thank you for your help in clarifying this matter.