it's an instruction for a processor (the heard of your pc) to process.

Opcode: Short for Operation Code.

An processor instruction usually consist of an opcode + some data used in the instruction. E.g. the instruction to call a sub-routine, consist of the CALL opcode + the ADDRESS of the sub-routine.
--
MiniMax

Kindof like the available commands on offer? Like commands in DOS (cd,copy,del etc).

Thank you all for the explanations. I´ve asked it because DosBox is showing me the following message, right after my game crashes and exit:

EXIT TO ERROR: CPU:GRP5:ILLEGAL CALL 7

I presume that this could be caused by one opcode not implemented yet. This one in particular could be fixed? Or do you need more info to solve this issue?

Thanks again.
Rcoltrane.

As written in the errormessage:
ILLEGAL call.
This isn't a valid opcode at all.
Probably some code goes wrong and and interrupt tables becomes cs:ip => leads ultimately to that error.

As Quoted from our faq:

1he CPU emulation encountered an instruction it doesn't emulate yet or and illegal instruction.
2This can mean the game uses some advanced CPU functions not emulated yet or something goes wrong and non-code gets executed.
3All in all nothing you can do anything about but wait for a newer version.