BPMN Tasks are the steps or actions taken to perform a specific piece of work — such as to enter a claim’s information into the line of business’ claim system, register a patient in a hospital, or enter an order for a project into a sales system. A number of logically related tasks can be combined into a higher‐level “Activity”.
A task may or may not have automated support. Some tasks can even be totally automated. These may be shown in a workflow model to provide information that helps staff understand what is happening. Tasks can also combine to form scenarios that are repeated based on events, timing, etc.
Source: Guide to the Business Process Management Body of Knowledge – ABPMP BPM CBOK V3.0.