A high-risk account is a bank account deemed to have a higher likelihood of being used for illicit activities like money laundering or tax evasion. Factors that can contribute to an account being classified as high-risk include the client's nationality, country of residence (CPI score below 50), occupation, source of funds, and the complexity of their financial transactions. Swiss banks are required to conduct enhanced due diligence on high-risk accounts to mitigate these risks.