Question

what does OP_DROP mean ??

Answer 1

It's a special code in an output script that means:

"Ignore what comes before this in terms of evaluating whether this output can be spent by the signature in an input."

It's how MultiChain embeds all sorts of special data in outputs without affecting the signature required to spend it.

Comments

i really didnt undersatnd

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You don't really need to worry about it unless you want to understand the internal workings of transaction verification. You can just consider it a marker for extra information that MultiChain added to the bitcoin protocol that it extends.