Professional liability occurs when a professional like an accountant or, I suppose in more common parlance, a doctor or a lawyer fail to perform their services in a way that’s required by professional standards. An easy example would be where a doctor operates on the wrong part of a body or a lawyer fails to bring a lawsuit before the statute of limitations runs out. And so for a CPA, common examples would be failing to file a tax return on time, failing to take advantage of a tax deduction that’s available for a client or some other impropriety, such as failing to detect miscue or misstatement in a client’s financial statements while doing an audit.