Liquidity. It’s one of the most frequently used words in finance. It gets invoked to explain virtually everything and anything. But it’s often clear that those invoking it are just parroting things they learned somewhere along the way and don’t truly grasp the mechanics of it. Most don’t even make the basic distinctions among its various forms.

Here’s a rough TL;DR of what you need to know:
1/7 There are three basic types of liquidity: Systemic, Credit, and Transactional.

Systemic liquidity can be loosely thought of as the unencumbered resources in the banking system that can be used to settle intra-bank payments. Think Fed funds. And if Fed funds breaks down, payroll doesn’t get made and ATMs run dry. This is what we were on the cusp of in 2008.

But, importantly, Fed funds is a closed system. A bank can draw on its reserves to meet payments to other banks in the system, or, when necessary, get physical cash, but it can’t ‘lend them out’ to clients. Nor can it flood the equity or currency markets with them–contrary to the popular trope. They are not fungible in that way. Only the Federal Reserve can add or withdrawal from the system (with that small exception of physical cash). So, while the composition of reserves across banks can change, the aggregate level in the system cannot unless the Fed wants it to. This type of liquidity is exogenous; it’s all about the Fed.
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