The start or completion of task is called 

Explanation

A few important definitions which are used in Project Management Techniques like CPM or PERT are specified below:

1. Event:  

• It is a stage that refers to a particular instant of time that indicates the starting or completion of an activity.
• The occurrence of an event neither requires time nor any other resources. Example: excavation started, beam cast is some events.

2.  Tail and End event: 

• An event that marks the starting of an activity called tail event and an event that marks the completion of an activity called end event.

3. Dual Role event: 

• An event that acts as both tail and end event is called a dual role event.

4. Activity: 

• It is the actual performance of the task which requires resources like time and cost for its completion.

5. Duration of activity: 

• Time taken for completion of a task is referred to as the duration of an activity.

6.  Dummy Activity: 

• An activity that never requires any kind of resources called dummy activity.  These activities are introduced in the network to establish logical and grammatical relationships between different activities.