Definitions of needs assessment may vary by purpose.
Curriculum and Training Development
A needs assessment is the process of collecting information about an expressed or implied organizational need that could be met by conducting training. (Source)
Needs assessment has been defined as the process of measuring the extent and nature of the needs of a particular target population so that services can respond to them. (Source)
An analysis of requirements. It
determines what people, functions or systems are currently lacking in
order to achieve the goals of an organization. A needs assessment also prioritizes the requirements so that the most glaring deficiency can be fulfilled first. (Source)