Activities are a special type of system entity. Create custom activity An action to be performed, such as a task, or a communication item that is sent or received, for example, e-mail, phone calls, and appointments. The status of activities is tracked and the activity history is stored in the system, so users can view the open and closed activities. entities to support your communication needs, including instant messaging (IM) and text messaging (SMS).
Because customizations affect all users, only a user with the System Administrator or System Customizer security role A defined set of privileges. The security role assigned to a user determines which tasks the user can perform and which parts of the user interface the user can view. All users must be assigned at least one security role in order to access the system., or equivalent permissions, can make customizations.
The data is split between two entities:
The Activity entity. The appropriately-named Activity entity stores information used in all activity types, such as the owner of the record. You cannot make changes to the Activity entity.
Custom activity entities. You create specific custom activity entities, such as E-mail, Task, and Letter. These store information specific to that type of activity. This information could be the courtesy copy (Cc) addresses used in an e-mail message.
When you create a customized activity entity, it is related automatically to the the Activity entity. When creating a custom activity, specify the entity as an activity entity (not to be confused with the Activity entity).
Because you cannot change the Activity entity, you cannot change the Activity entity form. Make your changes to a custom activity entity form.
You can create 1:N (one-to-many) relationships for a custom activity the same as any other activity. Also, you can update existing relationships.