Events are typically notifications created by an IT service, Configuration Item (CI) or monitoring tool.
The CIs are configured to generate a set of events based on the designer's experience.
Once an Event notification has been generated, it will be detected by the specific tool (read and interpreted) Filtering means that the event notification can be ignored or communicated to the management tool.
During the filtering step, the event will receive a level of correlation (type: informational, warning, or exception).
The filtering step is not always mandatory, some CI's have significant events that are communicated directly into the management tool (even if they are duplicated).