What's the difference between a task, a call report, and an appointment?

A task is a unit of work to be completed by one or more people. Tasks are related to business objects such as opportunities or contacts, and can include attachments.

An appointment is a calendar entry related to a business object, such as an opportunity or a customer. Appointments can include attachments.

A call report provides a historical view of all communications initiated by you to a customer, or by a customer to you. Call reports don't document internal communications.