Merge integrates with 2 types of "Ticketing" systems: traditional ticketing/project management platforms (Jira, Asana), and helpdesk platforms (ServiceNow, Intercom).
In the traditional ticketing platforms, contacts are typically not supported. Everyone with access to the platform is considered a User and is a known entity to the organization that owns it. They could be contractors, full-time employees, or even an auditor with temporary access.
In helpdesk platforms, Contacts represent entities, typically customers or people at a customer organization, that are reaching out to ask questions. If it is their first time reaching out, these entities may not be known to the organization that owns the helpdesk account. The Users in helpdesk platforms are typically "agents", or the employees responsible for responding to questions from the Contact.