If you send another person’s money to a different person, they effectively came from the same account and are therefore commingled. Your money is fungible, other people’s is not (unless you are a bank).
Some states have laws against floating, some do not.
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In many countries (including most states in the US), comingling funds between users is how you go to "jail" as it is usually a criminal offense.
see: Money Transmission laws
That by itself is not commingling. Money is fungible, and https://en.m.wikipedia.org/wiki/Float_(money_supply) is a well established and widely used concept.
If you send another person’s money to a different person, they effectively came from the same account and are therefore commingled. Your money is fungible, other people’s is not (unless you are a bank).
Some states have laws against floating, some do not.