A Trigger is a component which is responsible, based on an external input, for generating events which will initiate flows. Each running instance of a Trigger has a configuration, and uses this to decide what events should be sent to the Orchestrator.
A Trigger raises an event when something happens, and it is this something that makes each Trigger unique. For example, the something could be receiving a message from the Unit4 Message Hub (Message Hub Event Trigger), or an incoming Http request (Webhook Trigger).
Triggers can be related to a specfic source system, e.g. Unit4 Student Management, to all source systems in a Unit4 eco-system, e.g. Message Hub Event, or be independent of the Unit4 eco-system, e.g. Webhook Trigger, allowing Flows to be triggered from external Cloud Services like LogicApps.
Each Trigger can have its own minimum necessary configuration to be able to determine how it keeps track of the something happening. For example, the Message Hub Event Trigger has configuration which includes a Source System, a Tenant (automatically populated based on user's tenant and only visible for tenant administrators), a Message Type (Document or Event), a Name, and a Version.
Trigger configurations can be shared with more than one Flow