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

Tickets can be grouped into Collections. Collection resource usually maps to the various grouping systems used in the underlying product. Some examples are lists, projects, epics, etc. You can differentiate between these grouping systems using the type attribute of a Collection.

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.

Tags represent a common classification approach used in various ticketing systems. A Ticket may have one or more Tags associated with them.

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 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.