A Java Compiler is a program that translates Java source code, written in plain text, into bytecode, which is a set of instructions that the Java Virtual Machine (JVM) can execute. This process allows developers to write code in a human-readable format, which the compiler then converts into a format that can be run on any device that has a JVM, ensuring cross-platform compatibility. The most commonly used Java Compiler is part of the Java Development Kit (JDK), known as `javac`. When a developer runs `javac` on a Java file, it checks the code for errors and generates a `.class` file containing the bytecode. This bytecode can then be executed by the JVM, allowing the program to run on various operating systems without modification.