In the context of software, a library refers to a collection of pre-compiled routines or functions that a program can use. These libraries provide a way to reuse code and thus make software development more efficient and manageable. Typically packaged as a single file, a software library can offer a range of functionalities from mathematical calculations to more complex operations like network communication or image processing. By relying on established libraries, developers can focus on the unique aspects of their application, avoiding the need to 'reinvent the wheel' for every new project. Libraries can be either static or dynamic; the former is included as part of the final executable file, while the latter is loaded as needed during runtime. Overall, libraries are crucial for code modularity, reusability, and maintainability in software engineering.