In short, US net liquidity is the amount of Treasuries and (less so) mortgage-backed securities held in the coffers of the Federal Reserve and the US Treasury. -- This number tends to directionally correlate with US-based assets, such as micro-, small-, and mid-cap US equities.

M2 is the estimated total amount of money supply, including checking/savings accounts, physical cash, and CDs. -- This number tends to directionally correlate with the movement of global assets, such as bitcoin, gold, and megacap stocks.