As mentioned earlier, it is one or more Symptom Definitions that defines when an alert is triggered. There are four different Symptom Definition types:
If you are creating your own custom alerts, you will generally be working with Metric/Property Symptom Definitions. The other three are generally used by vRealize Operations itself, or by Solutions.
The description of every symptom includes its Criticality. This is a measure of how important the symptom is. There are four levels of Criticality: