What does M2 stand for?

Could you please clarify what M2 stands for in the context of finance and economics? I've heard it mentioned in discussions about monetary policy and money supply, but I'm not entirely sure of its precise definition. I'm particularly interested in understanding how it differs from other monetary measures like M1 and how it's calculated. Additionally, I'd like to know the significance of M2 in terms of its impact on the economy and how policymakers might use it to inform their decisions.