Tight coupling refers to a situation in software design where different components or modules are highly dependent on each other. This means that changes in one component can significantly affect others, making the system less flexible and harder to maintain. For example, if a function in a program relies on specific data formats from another function, any change in that format could break the entire system. In contrast to loose coupling, tight coupling can lead to challenges in scalability and testing. When components are tightly coupled, developers may find it difficult to isolate and test individual parts of the application. This can slow down development and increase the risk of introducing bugs when modifications are made.