What best describes a library in programming?

In programming, a library refers to a collection of pre-written code that can be reused by developers to perform common tasks, functions, or algorithms without needing to write them from scratch. Libraries provide a way to encapsulate and organize code in a manner that makes it easier to maintain and share, allowing programmers to leverage existing solutions for common problems.

For instance, when you want to perform mathematical computations or handle data structures, you can use libraries that contain various functions and classes to simplify your code. This not only saves time but also reduces the risk of errors since these libraries are typically well-tested and widely used in the programming community.

The other options do not accurately capture the essence of what a library is in programming. A collection of variables, a single code file, or a database of user information do not encompass the broader and more functional concept of a library, which is fundamentally designed to provide reusable code segments for developers to utilize in their own programs.