A standard library (also called a class standard library) is a collection of classes and interfaces available for all implementations of the language. In simpler terms, this means that, it is a collection of .class files included in the JDK and ready to be used. Once you have installed Java, you get them as part of the installation and can start building your application code up using the classes of the standard library as building blocks that take care of a lot of low-level plumbing. The standard library's richness and ease of usage substantially contributed to Java's popularity.
These collections are organized by packages. That's why instead of saying Java standard library, which would be the correct way to refer to all these collections together, programmers call them Java standard libraries – because, in order...