A Preferential Trade Area (PTA) is a stage of economic integration. It is often brought about by a Preferential Trade Agreement.
In a PTA, each member treats each other at least as well as they treat any other nation. In other words, the members give each other Most Favored Nation status.
For instance, imagine there are three nations: A, B, and C. A and B are in the PTA, C is outside it. A has to make sure its tarrifs on B's goods are not higher than its tarrifs on C's goods. Likewise, B has to make sure its tarrifs on A's goods is no higher than tarrifs on C's goods. Whether or not nations outside PTAs are absolutely hurt is hotly debated.
A PTA is a often considered non standard, because they can form spontaneously. Additionally, one of the greatest arguments against economic integration is that it reduces national sovereignty, and this effect is completely lacking at this stage.
The most successful PTA in history is the World Trade Organization. However, it is not a "pure" PTA. The WTO allows its members to form special relationships, as long as they are FTA, CU, CM, EU, or MU | 
