In the 6502 and Z80, "opcode" refers to the actual machine instruction executed by the CPU, represented by mnemonics (e.g., LDA, STA). Each mnemonic can map to multiple opcode values due to different addressing modes.

The 6502 has 56 mnemonics, mapping to about 151 unique opcodes.

The Z80 has about 80 distinct mnemonics, mapping to about 158 base opcodes, with extended opcodes (via CB, ED, DD, FD prefixes) pushing the total to around 500.

Java bytecode opcodes are symbolic instructions for a virtual stack machine, about 200 in total with a 1:1 mapping from mnemonic to opcode, and just an "wide" extended prefix to extend operand sizes, designed for portability rather than direct hardware execution.