The written output of a needs assessment: the gap an organisation has to close, described with no product, technology or supplier named in it.
A statement of need records the gap itself rather than the answer to it. The test of a good one is that it survives the failure of any particular solution: if the wording would have to change because a supplier withdrew or a technology turned out to be unsuitable, what was written was a specification. It carries a date, because a gap measured long before funding arrives describes a state the organisation has usually since moved away from. Options, costs and a recommendation belong in the business case that follows it.
See also
Structured work establishing the gap between an organisation's current state and the state it requires, in evidence, before any solution is named.
The document justifying an investment, evaluating the benefit, cost and risk of alternative options and giving a rationale for the preferred one.