In object-oriented programming, a class is said to inherit from another class when it is based the implementation of that class. In this case, the subclass inherits all the members (properties, methods, events and callbacks) of the superclass.
All classes in the ROBLOX object system inherit, directly or indirectly, from the Instance class. Many classes inherit from structural classes that provide members common to all their subclasses. This is the case for Part, WedgePart, TrussPart and VehicleSeat, which all inherit from BasePart.