The Java Compiler API is a part of the Java Development Kit (JDK) that allows developers to compile Java source code programmatically. It provides an interface for interacting with the Java compiler, enabling applications to compile Java code dynamically at runtime. This is particularly useful for tools that need to generate or modify Java code on the fly. Using the Java Compiler API, developers can create custom compilers or integrate compilation features into their applications. It supports features like error reporting and can be used alongside other Java libraries, such as Java Reflection and Java Annotations, to enhance functionality and streamline development processes.