Objective-C is a general-purpose, object-oriented programming language that was the primary language used for developing applications on Apple's macOS and iOS platforms before the introduction of Swift. It is a superset of the C programming language, adding Smalltalk-style messaging and dynamic runtime features. Objective-C is known for its unique syntax, which incorporates square brackets for method calls, and its support for object-oriented concepts like inheritance, encapsulation, and polymorphism. Although largely replaced by Swift for modern Apple development, Objective-C remains important for maintaining legacy applications and frameworks.