How many drinks is one Cosmo?

Excuse me, could you please clarify something for me? I'm trying to understand the measurement of drinks when it comes to Cosmos. I've heard people talking about having 'one Cosmo' but I'm not quite sure what that means. Is 'one Cosmo' referring to a specific volume or quantity of the drink? Is it a standard measurement like a shot or a glass? Or does it depend on the bar or the person serving it? Could you possibly give me a rough estimate of how many ounces or milliliters a 'one Cosmo' typically contains? Thank you for your help in clarifying this matter for me.