The NIB file extension is primarily associated with Apple's development environment, specifically used by Interface Builder, a tool integrated within Xcode (and previously as a standalone application). NIB stands for NeXT Interface Builder, stemming from Apple's history with NeXTSTEP. These files are binary archives that store the user interface (UI) layout, design elements, and connections (outlets and actions) for applications developed for macOS, iOS, iPadOS, watchOS, and tvOS. A NIB file essentially defines the visual structure of a window, view, or other UI component. When an application launches, the corresponding NIB file is loaded by the system to construct the graphical interface the user interacts with. While modern Apple development often favors using Storyboards (.storyboard files) or SwiftUI, NIB files remain relevant for legacy projects or specific custom view configurations. They contain serialized objects representing UI elements like buttons, text fields, tables, and their associated metadata and linking information.