SOC: security operations
A security operations centre brings together the people and processes that monitor, investigate and escalate security activity. Its value depends on the coverage, quality and authority of that operation.
SIEM: the technology platform
Security information and event management platforms collect and analyse logs. They support detection and investigation, but require suitable data, well-maintained rules and people who can interpret the results.
MSSP: the service provider
A managed security service provider delivers agreed security services for a customer. The exact combination of monitoring, tooling, engineering and response depends on the contract.
Ask about the complete service
Rather than buying an acronym, establish which systems are covered, who performs each task, when support is available and what your organisation must still do.