Bytecode is an intermediate representation of code that is generated by a compiler from high-level programming languages like Java or Python. It is not directly executed by the computer's hardware but instead runs on a virtual machine, such as the Java Virtual Machine (JVM). This allows for platform independence, meaning the same bytecode can run on different systems without modification. When a program is executed, the virtual machine interprets the bytecode and translates it into machine code that the hardware can understand. This process can improve performance and security, as the bytecode can be optimized and checked for errors before execution.