Dynamics CRM platform uses the term Entity (commonly known to developers as Tables) to store the information about specific type of record. The platform installation creates about 260 system entities. Custom entitie(s) (aka Custom Table(s)) can be created to address the needs of the organization.
There are two options available for Entity Ownership viz., User or Team and Organization.
User or Team Ownership > This will add a new field called Owner that facilitates assigning the Entity between Users and Team.
Organization Ownership > There will no Owner filed created and hence cannot be assigned between Users and Team.
Activity Entity: While creating a custom activity there is the option to create the entity as an activity. This allows the entity to appear in UI in other locations.
The following screen shots show form for creating new Custom entity and the table created in [Organization]_MSCRM database: