Economists studying the money supply categorize the status of the money based on?

They categorized the status based on Liquidity

Liquidity describes how easy that money can be used for a quick payment without necessarily affect the overall value of the assets.

For example we have 10,000 in cash. If that cash is retained to pay a $ 10,000 Debt to another company, that cash is categorized as non liquid, which meant we can't really use it even though we had it