Alert correlation is a type of log analysis. It focuses on the process of clustering alerts (events), generated by NIDS and HIDS computer systems, to form higher-level pieces of information. Example of simple alert correlation is grouping invalid login attempts to report single incident like "10000 invalid login attempts on host X".
See also ACARM ACARM-ng Bottom-up and top-down approaches OSSIM Prelude Hybrid IDS Snort
References