A clause setting out how, to whom and by when a party must formally communicate something for it to count. Missing the deadline can forfeit the entitlement.
A notice provision usually specifies three things: the route a formal communication must take, the named recipient it must reach, and the period within which it must be sent, commonly measured from the moment a party became aware of the event rather than from the event itself. The consequence of missing it is disproportionate to the effort of meeting it, because a sound entitlement can lapse purely on the mechanism. Responsibility for a notice arriving generally sits with the sender, so telling your usual contact or raising it at a meeting does not discharge the obligation.
Where this comes up
A delivery manager does not need to know contract law. They need to notice the moment a delivery problem becomes a contractual one, because after that moment informal handling starts costing money.
A make or buy analysis compares the whole life cost of building something against buying it, and finds the point where the cheaper option changes. Capability, control and risk usually decide it.