The actual performance of a task is called an Activity.

An activity is the actual performance of a task. The preceding event is called the "tail event and the following is called the "head event'.

The activities are classified into four categories

Predecessor activity:- Activities that must be completed immediately prior to the start of another activity are called predecessor activities.

Successor activity:- Activities that can't be started until one or more of the activities are completed but immediately succeed them are called successor activities.

Concurrent activity:- Activities that can be accomplished simultaneously are known as concurrent activities.

Dummy activity:- An activity that does not consume any resource but merely depicts technological dependence is called a dummy activity.