Accounts represent the companies or organizations that you are in contact with. Accounts have one or more Contacts associated with them.

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.

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.

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