Free trade is a term meaning unregulated trade between nations without tariffs or quotas placed on the goods exchanged. This is generally a positive thing as it allows countries with an Absolute advantage, such as China, to cooperate with its neighbors and produce more goods than either country could in isolation.
Free trade is controversial because it can have undesired side effects, such as a massive loss of manufacturing jobs by the wealthier trading partner though a mechanism known as "offshoring" those jobs to a trading partner having cheaper labor. In economics, this is known as a market correction.
Free trade also raises moral issues, such as the use by a nation of slave-labor. In addition, free trade can increase the importation of undesired, concealed illegal drugs.