An activity is a step or location in your business process that you select to monitor.
Activities are generally an event-driven process that satisfy some business objective or goal. Activities in your transaction pathway are often points in your business where complex logic is used to route transactions to one or more places concurrently, or critical points in the IT infrastructure that are suspected of performing poorly.
Adding an activity to a point in a transaction pathway allows you to monitor or capture information about what happens at that point in your business process. Some typical activities might be:
Reviewing customer data
Evaluating transaction value (and filtering on it)