Money laundering is the practice of disguising the origins of illegally-obtained money, by which the proceeds of a criminal activity are made to appear ligit.
The money involved can be generated by any number of criminal acts, including drug dealing, corruption, accounting and other types of fraud, and tax evasion. The methods by which money may be laundered are varied and can range in sophistication from simple to complex.
There is no minimum threshold of money, nor is there the requirement that the transaction succeed in actually disguising the money.
Merely passing money from one person to another, so long as there is intent to disguise the source, ownership, location or control of the money, is considered a financial transaction under the law.