What is meant by extensions in the context of programming or systems?

In programming and extension systems, extensions are additional modules or components that add new capabilities or functions to an existing application or platform without modifying its source code.

For example, in iOS, extensions allow applications to interact with the system and other apps, providing widgets, keyboard extensions, actions in the context menu, etc. This helps to expand functionality and improve user experience.

Example: the keyboard extension in iOS allows users to use alternative keyboards in different applications.