"Bytecodes" is a name given to the instructions of the Java VirtualMachine, so called because the opcodes are 8 bits (one byte) in length, and instructions vary from one to several bytes in length. Bytecodes are found in Java .class files.

Bytecode instructions perform a similar job to native machine instructions, except that bytecodes are machine independent. They are compact (1.8 bytes per average instruction is claimed, though this neglects overheads such as the constant pool). Some bytecode instructions are quite high level, e.g. dynamically invoking a virtual method by name).

-- MikeVanEmmerik - 01 Dec 2001