It is an amount owed - not to the bank, as is commonly believed - but to, for example, ANAF (National Agency for Tax Administration), DITL (Directorate of Local Taxes) or a bailiff. 

It may be a forgotten tax payment - as an individual or company. Because, after all, we all owe a tax 😊 at some point. 

And yes, we do fall behind on payments for various reasons, even though paying taxes can be done very easily online by card. And unfortunately blocking the amounts in your accounts means you can no longer withdraw money from branches or ATMs, nor can you make transfers or payments 😞