The silence is a setting available on an agent or a metric that allows you not to receive any notification from the agent or the metric during the defined period. You can create a new silence, edit or delete the existing ones, for that you have to click on 🔔.
This an example of a dashboard view and you can see the silence button to the right of each metric :
To create a silence you click on the 🔔 of the chosen metric or the agent for the silence after that, a page like this appears. You need to fill in the Reason field and setup the start and the end date of the silence :
To edit or delete a silence you click on the 🔔 of the chosen metric or agent and after that you click on an event in the calendar.
This is an example: