Structuring, also known informally as "smurfing," is a crime in which bank transactions are spaced out to avoid going over thresholds that would trigger government mandated reporting requirements imposed on financial institutions in order to uncover other crimes such as money laundering and tax evasion.
Under US law, structuring is considered a felony. Intent to evade reporting requirements is not required to be found guilty of the crime of structuring, and as with any other law, ignorance of the law is not a valid defense.
In the US, banks are required to report any single deposit or withdrawal of funds larger than $10,000, so structuring in a US context would involve making several deposits or withdrawals in a row of less than $10,000. However, while the $10,000 reporting requirement is widely known, unbeknownst to many, banks are also required to report any suspicious activity that looks like structuring, an additional requirement which generates around 700,000 reports per year. Banks not only do not have to tell people if they are being reported as suspected structurers, but in fact are legally barred from doing so.
Structuring is an important crime to know about because many seemingly innocent people are reported for structuring each year. In many of these cases, although the individuals involved did not intend to commit a crime, they *did* in fact deliberately structure their deposits or withdrawals. This is because the $10,000 limit is widely known, so many people think that even though they are not involved in criminal activity, they should avoid going over that threshold based on the notion of "better safe than sorry." Ironically however, they are actually being less safe, and more likely to be sorry, and under the letter of the law, would in fact be guilty of the federal crime of structuring.
The bottom line is, if you are not involved in criminal activity, there is absolutely no reason to structure your bank transactions to be less than $10,000, and in fact you should never do so, because it is actually illegal.