In plain English
A popular Fed “net liquidity” recipe: the Fed’s total assets, minus the Treasury’s checking account at the Fed, minus money-market cash parked at the Fed overnight.
In words: how much of the Fed’s balance sheet is actually sitting in the banking system as reserves. Rising has often been easier for risk assets; falling is QT plus drains. Lag chips slide the liquidity line forward so you can see the lead with your eyes.