The `select()` function is a system call used in programming to monitor multiple file descriptors, allowing a program to wait for events on these descriptors. It is commonly used in network programming to handle multiple connections simultaneously without blocking. When a file descriptor is ready for reading, writing, or has an error, `select()` notifies the program, enabling efficient input/output operations. In the context of the Unix operating system, `select()` can manage sockets, pipes, and other I/O streams. It takes three sets of file descriptors as arguments: one for reading, one for writing, and one for exceptions. This functionality is crucial for building responsive applications that interact with multiple data sources.