A "data breach" refers to an incident where sensitive and confidential information is accessed, disclosed, or stolen without authorization. This can involve personal information, financial data, or intellectual property, and may occur through hacking, malware, or insider threats. The consequences of a data breach can be severe, including loss of customer trust, legal penalties, and financial losses. Organizations must implement robust security measures to mitigate the risks of data breaches and ensure compliance with regulations like the General Data Protection Regulation (GDPR).