Security Incident and Event Management (SIEM) is a term or acronym related to Cybersecurity which also includes several variants; SEM, SIM (often used interchangeably) that refer to real-time monitoring, collection and correlation of cybersecurity events, notifications and console views. for the purpose of identifying cybersecurity threats events and threats. Long-term storage and analysis, manipulation and reporting of collected log data and security events records is required which is known as security information management (SIM) and as you can infer by putting this together you have security information and event management or (SIEM).
SEIM data is typically monitored by a Security Operations Center or (SOC) who can provide with Incident Response to detected cyber threats.