alert definition
Alert definitions define when to trigger an alert and for which entity. See Alert Definitions
alert condition
Python expression defining the “threshold” when to trigger an alert. See Condition.
check command
Python expression defining the value of a check. See Check Command Reference.
check definition
A check definition provides a source of data for alerts to monitor. See Check Definitions
A dashboard is the main monitoring page of ZMON and consists of widgets and the list of active alerts. See Dashboards
In ZMON, downtime refers to a period of time where certain alerts/entities should not be triggered. One use case for downtimes are scheduled maintenance works. See Downtimes
Entities are “objects” to be monitored. Entities can be hosts, Zomcat instances, but they can also be more abstract things like app domains. See Entities
JavaScript Object Notation. A minimal data interchange format. You probably already know it. If you don’t, there’s good documentation on its official page.
A simple markup language that can mostly pass for plain text. There’s an introduction and a syntax reference on its official page.
time period
Alert definition’s time period can restrict its active alerting to certain time frames. This allows for alerts to be active e.g. only during work hours. See Time periods

Not actually Yet Another Markup Language. A powerful but succinct data interchange format. This document should be sufficient to learn how to use YAML in ZMON. In case it isn’t, the Wikipedia entry on YAML is actually slightly more useful that the official documentation.

Note that YAML is a strict superset of JSON. That is, wherever YAML is required, JSON can be used instead.