In money laundering a suspicious transaction can be a lot of different things.
However most times a suspicious transaction can be as simple as a very large deposit or multiple large deposits by an individual or even a business that doesn't regularly make those large deposits.
Some money laundering people make multiple deposits of $10,000.00 or more or sometimes less and if the deposits get irregular then the bank may see it as suspicious and then investigate.
You can deposit any amount of money you want too in a bank account however banks must and will report large transactions to the IRS of $10,000.00 or more because they are required too by law.
So if you deposit $10,000.00 or more into your checking or savings account then it will be reported to the IRS and then they might audit you.
If you've never deposited $10,000.00 or more into your bank account and then suddenly start depositing $10,000.00 or more into your bank account then the bank may see that as suspicious and investigate.
It is possible to legally start making $10,000.00 per month or more and then suddenly deposit the money into a bank account.
So it's not always a problem and if you got the money legally then nothing will happen to you other than you might get audited by the IRS.