What break-in means
When an engine is new or has been rebuilt, its internal surfaces have not yet settled into their final working pattern. During the first period of running, the piston rings seat against the cylinder walls and other moving parts bed in. This period is commonly called break-in or running-in, and the oil present during it is sometimes given that name.
The idea of a dedicated break-in oil comes mainly from engine rebuilding and performance work. There, a builder may call for an oil with a specific additive package, often higher in certain anti-wear additives, to protect parts such as a flat-tappet camshaft while they bed in. That is a deliberate choice tied to a particular build, not a general rule for every car on the road.
The factory fill on modern cars
Most modern production engines leave the factory with an oil chosen by the manufacturer to suit break-in and normal use alike. This factory fill is part of the engineering of the car, and the maintenance schedule is built around it. For the great majority of new cars, that means the first oil is meant to stay in place until the first scheduled service interval listed in your owner’s manual.
Older advice to change the oil very early, after a few hundred miles or kilometers, generally does not apply to current vehicles unless the manufacturer says so. Some manuals do specify a shortened first interval, and a few engines have particular instructions, so the manual is always the deciding source.
When to change it
Change the factory fill at the point your manual gives, using the viscosity grade and specification it lists. Do not bring that change forward on assumption alone. If you have a rebuilt or performance engine, follow the engine builder’s instructions instead, since they know what oil that build needs and when it should first be drained. When the manual and the builder agree on timing, that is your schedule; when in doubt, ask whoever specified the engine before changing early.