What does XMR stand for?

Could you please clarify for me the acronym "XMR"? I've seen it mentioned in several contexts related to cryptocurrencies, but I'm not quite sure what it stands for. Is it a specific type of coin or token? Or does it represent a particular aspect or feature within the crypto world? Any additional information you could provide would be greatly appreciated. I'm trying to expand my knowledge in this area and understand the various terminologies used. Thank you in advance for your assistance.