Who is invitation code?

Could you please clarify who or what you mean by "invitation code" in the context of cryptocurrency and finance? Are you referring to a unique code that is used to invite someone to join a specific platform, exchange, or service within the crypto ecosystem? If so, such codes are often offered as a way to incentivize new users to sign up and can sometimes provide benefits like reduced fees, exclusive access, or even a small amount of free cryptocurrency. Is there a specific aspect of invitation codes you'd like to learn more about?