Java bytecode is an intermediate code generated by the Java compiler after the compilation of source code written in Java. It is essentially the machine-level code that runs on the Java Virtual Machine (JVM), acting as an instruction set for the JVM. The bytecode is generated in the form of a .class file, which is a non-runnable code that requires an interpreter to execute. The interpreter, also known as the JVM, executes the bytecode on the system. The bytecode is the common piece between the compiler and the interpreter, and it makes Java a platform-independent language.

When a Java program is compiled, the compiler converts the source code into bytecode or machine code. The JVM then interprets the bytecode and executes it on the system. The JVM is stack-based, so it uses a stack implementation to read the bytecode. The bytecode is a set of instructions for the JVM, and it is equivalent to an assembler in C++.

Java programmers do not need to be aware of or understand Java bytecode at all, but understanding bytecode and what bytecode is likely to be generated by a Java compiler can help Java programmers in the same way that knowledge of assembly helps C or C++ programmers. Some projects provide Java assemblers to enable writing Java bytecode by hand, and assembly code may also be generated by machine, for example, by a compiler targeting a Java virtual machine.

In summary, Java bytecode is an intermediate code generated by the Java compiler after the compilation of source code written in Java. It is essentially the machine-level code that runs on the Java Virtual Machine (JVM), acting as an instruction set for the JVM. The bytecode is generated in the form of a .class file, which is a non-runnable code that requires an interpreter to execute. The interpreter, also known as the JVM, executes the bytecode on the system. The bytecode is the common piece between the compiler and the interpreter, and it makes Java a platform-independent language.