I just went to a really interesting meeting where the head of fraud for one of the major banks presented their approach to money mules.
Pic from eCybercrime
A money mule is a bit like a drugs mule, someone who is carrying out illicit activities on behalf of others.
His definition is that a money or cashout mule is one where an account is “used to receive fraudulent funds form a third party victim. The individual involved may or may not be complicit in the crime: