What is the difference between a normal execution thread and the main thread in a program?

The main thread is the primary execution thread of a program, usually responsible for initializing the application and interacting with the user interface (UI).

Regular (additional) threads are created to perform tasks in parallel with the main thread to avoid blocking the UI and to improve the application's responsiveness.

For example, in iOS, all UI updates must occur on the main thread, while long-running operations (data loading, calculations) are recommended to be performed on a background thread to prevent UI slowdown.

Thus, the main difference is in their purpose and role: the main thread manages the UI and the application's lifecycle, while regular threads are used for background tasks and parallel processing.