The Role object represents a role of a User.

The User object represents a User.

Attachments are the files associated with a ticket or a comment.

Comments represent the communication happening on a Ticket, both between a User and a Contact and the internal things like notes, private comments, etc. A Ticket can have one or more Comments.

Contact represent the external people you are in contact with. These could be customers, leads, etc. Contacts can be associated with an Account if the underlying product supports it.

Core resource which represents some work that needs to be carried out. Tickets are usually mapped to issues, tasks, work items, etc. depending on the underlying product.

Ticket Types represent the classification system used by the underlying products for Tickets. Some examples are bugs, feature, incident, etc.

Fields represent the attributes defined for various entities in the underlying product. Depending on the underlying product, custom attributes can be defined by a User on various entities like Ticket, Contact, etc. is_user_defined attribute within Field can be used to differentiate between custom and system defined Fields.

Ticket Status represents the completion level of the Ticket. Some products provide customizing the Ticket Status.

Ticket Priorities represent the intended order in which the Tickets should be worked on. Some products provide customizing the Ticket Priorities.

Users represent the people using the underlying ticketing system. They are usually called agents, team members, admins, etc.