The named group holding authority to approve or reject a change request, and the only body that can move an approved change into the baseline.
A change control board is an authority rather than a meeting, and the distinction matters when the meeting is skipped. What makes it work is that its membership is named, its decision is recorded, and its remit states which categories of change it can settle on its own and which it must pass upwards. Boards fail in one of two ways: they approve everything, in which case they are a logging exercise, or they sit at the wrong altitude and find themselves ruling on baseline changes that should have gone to whoever holds the money. A board whose approvals nobody can trace back to a person has provided reassurance rather than control.
See also
A change request that realigns future work with the plan after performance has already drifted away from it.
The approved, time phased budget a project is measured against, made up of the priced work packages plus their contingency reserve, and excluding management reserve.
Where this comes up
Predictive work gets an ending for free, the day the thing is handed over. Iterative work has to manufacture one, which is why so much of it never formally ends at all.
Three types, separated by one variable: how much authority the office holds. Supportive advises, controlling requires, directive runs the work. Level is a second axis and a different question.