What is an M2 measurement?

Excuse me, could you possibly elaborate on what exactly an M2 measurement represents in the realm of finance and economics? I understand it's a monetary aggregate, but I'm curious about its specific composition and significance in terms of assessing the overall money supply and its potential impact on economic activity. Additionally, how is it different from other monetary aggregates like M1, and why is it considered an important indicator by policymakers and financial analysts?