meaning of laundered

[Learning_English]

the money trail = when money is being "laundered" for illegal reasons, it is moved from account to account. This is known as money trail. snails leavel a trail of slime that you can follow; money transactions leave a trail of evidence that you can follow.

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[Conchita]

launder (MONEY)
verb [T]
to move money which has been obtained illegally through banks and other businesses to make it seem to have been obtained legally:
Officials were accused of laundering the stolen funds overseas before returning them to the US.

(from Cambridge Advanced Learner's Dictionary)

A trail of slime = tracks or marks of sticky liquid (such as those left by a snail).

A trail of evidence = traces of crime.