A Business Impact Analysis (BIA) is an assessment of an organization’s business functions to develop an understanding of their criticality, recovery time objectives, and resources needed. By going through a Business Impact Analysis, the organization will gain a common understanding of functions that are critical to its survival.
A risk assessment is an evaluation of the exposures present in an organization’s external and internal environments. A Business Assessment generally include Business Analysis as a discipline and it has heavy overlap with requirements analysis sometimes also called requirements engineering, but focuses on identifying the changes to an organization that are required for it to achieve strategic goals. These changes include changes to strategies, structures, policies, processes, and information systems. A disaster recovery plan is the comprehensive statement of consistent actions to be taken before, during and after a disruptive event that causes a significant loss of information systems resources.
Source: BARNES, James C. & ROTHSTEIN, Philip J., A Guide to Business Continuity Planning, John Wiley & Sons, 2001 (page 57).