Acropolis - The high point or citadel of an ancient Greek city, like the Acropolis in Athens. It is generally a raised area above the rest of the city where the most important sacred and secular buildings are brought together. The buildings on the Athenian Acropolis were important for trade and worship.
Bitcoin is a digital currency (also called crypto-currency) that is not backed by any country's central bank or government. Bitcoins can be traded for goods or services with vendors who accept Bitcoins as payment.
Bitcoin is a payment system invented by Satoshi Nakamoto, who published the invention in 2008 and released it as open-source software in 2009.