Deployment Event Triggers
Deployment event triggers listen to events from status event sources and deployment providers to start releases. Each time a Deployment provider application that existing Live Deployments in the Release server changes its state, the trigger will start a release from the template that is associated with the trigger.
Webhooks Overview
Webhooks, introduced in Release 9.7, are able to trigger releases as a reaction to specific HTTP requests made by an external source. This can potentially reduce the load of Release, while also reducing the pressure on external systems caused by polling methods where release triggers had to actively make requests to the third party system.