What is black card used for?

Could you elaborate on the purpose and usage of a "black card" in the context of cryptocurrency and finance? I'm curious to understand if it refers to a specific type of premium financial service, a specialized payment method, or perhaps a tool for managing high-value transactions. Additionally, I'm wondering if it's a widely recognized term in the industry or if it's more of a colloquial reference. Could you clarify the specifics of how a black card might be utilized and its potential benefits or drawbacks for users?