You can add hidden field to ui_component xml file with formElement=”hidden”.
The hidden field is used for mostly for an entity_id field.
Entity_id field is used to fetch the records of a specific object.
<field name="entity_id" formElement="hidden">
When you check the UI component field using Browser Console, Its available but it’s not visible to the form.
A hidden field is used to post the data to the server with value.