Program libraries are a collection of pre-written codes, routines, and functions that can be utilized by a software developer in their programming work to save time and optimize the program. There are several synonyms for program libraries, such as code libraries, software libraries, libraries, or just 'libs'. They all refer to the same concept- a collection of pre-written codes or functions that developers can easily access. Program libraries can be customized to serve specific programming needs, and they are essential tools that developers use to program efficiently and effectively. These libraries can be used for a variety of programming languages and can make programming less time-consuming and more consistent.