Central bank is economical institution, which is seen as essential part of the contemporary economics. One of its many functions includes implementation of the monetary policy - namely regulating amount of money circulating in the market (i.e., printing of money). Most commonly it is said that first contemporary central banks emerged by the end of XVII century (starting from England), though there were attempts at creating something similar during the middle ages.
Before the central banks value of money were based on the value raw products (e.g., gold) used to produce a coin. Namely everything was based on a belief that a coin might be melted down and traded for a similar value. This principle is behind the money in Westeros, but the author of the forbes.com article considers the possibilities to create central bank in Westeros. The article is an interesting read to both fans of the show (or books) as well as to the people interested in how central banks emerge and what do they do.