Mercantilism was an economic system of trade that spanned from the 16th century to the 18th century. Mercantilism is based on the principle that the world's wealth was static, and consequently, many European nations attempted to accumulate the largest possible share of that wealth by maximizing their exports and by limiting their imports via tariffs.
Laissez faire is the belief that economies and businesses function best when there is no interference by the government. It comes from the French, meaning to leave alone or to allow to do. It is one of the guiding principles of capitalism and a free market economy.