"MOC" in CoreData refers to a managed object context.
A context consists of a group of related model objects that represent an internally consistent view of one or more persistent stores. Changes to managed objects are held in memory, in the associated context, until that context is saved to one or more persistent stores. A single managed object instance exists in one and only one context, but multiple copies of an object can exist in different contexts. Thus an object is unique to a particular context.
... is not actual code, it's just representing that the initialization of the managed object context would go there.
let moc = NSManagedObjectContext(concurrencyType: .mainQueueConcurrencyType)