A bank levy is what happens when your bank account gets frozen while the money in your account gets taken away from you. This normally happens when you do not pay your taxes or debt.
Normally, it is government agencies (like the IRS) that make use of a bank levy, using it to collect unpaid taxes. They will freeze your account and they take money equal to the amount that is owed. When your account is under a bank levy, you will not have access to your funds until the entire debt is paid back.