Atomic properties ensure thread-safety by locking the property, making it slower. Nonatomic is faster but not thread-safe and is generally preferred for performance reasons.

MVC stands for Model-View-Controller. The Model represents data, the View displays the user interface, and the Controller acts as an intermediary between the model and the view to process user input and update the UI.

A delegate is a design pattern that allows one object to communicate back to another object when a specified event occurs. It is typically used for handling events like user interactions.

A closure in Swift is a self-contained block of functionality that can be passed around and used in your code. Closures can capture and store references to constants and variables from the context in which they are defined.

Memory management in iOS is handled through Automatic Reference Counting (ARC). ARC automatically tracks and manages the app's memory by counting the references to objects and deallocating them when the reference count is zero.

GCD is a low-level API for managing concurrent operations by dispatching tasks across multiple threads. Operation queues are a higher-level abstraction that allows for more control over the execution and dependencies of queued tasks.