An activity is a sub-set of process. For example, new business process in Insurance industry can comprise of activities such as Application Data Entry, Underwriting, and Policy Issuance. Whereas an event is an occurrence or an outcome which is of significance, and based on which typically, a business rule can be triggered. For a example, an event could be start of an activity, end of an activity, non-completion of an activity within a certain timeframe, etc.