Javac is a command-line tool used to compile Java source code into bytecode, which can be executed by the Java Virtual Machine (JVM). It takes files with a .java extension as input and produces .class files as output, enabling Java programs to run on any platform that supports the JVM. The Java programming language, developed by Sun Microsystems, is known for its portability, allowing developers to write code once and run it anywhere. Javac is an essential part of the Java Development Kit (JDK), which provides the necessary tools for developing Java applications.