A targeted employment area (TEA) is a rural area or an area that has experienced high unemployment. A high unemployment area is an urban area where the unemployment rate is at least 1.5 times the national average. See USCIS official definition here.
TEA status is important because if the EB-5 project is located in a TEA, then the investment amount is reduced from $1 million to $500,000.
To demonstrate that a project is located in a TEA, the EB-5 investor must provide with their I-526 petition evidence of the unemployment rate of the metropolitan statistical area or county in which the project is located, or more typically, a letter from a state government that the area qualifies as a TEA. This "TEA letter" is provided to the investor by the Regional Center.
The EB-5 investor must show their investment was made in a TEA-qualified project at the time of filing the I-526 petition or at the time of making the investment. (The difference is based on whether the EB-5 capital is made available to the project at the time of filing the I-526 petition.) The EB-5 investor does not need to prove that their investment qualifies as a TEA when filing the I-829 petition for the permanent green card. Thus, the EB-5 investor is not penalized for the economic growth of the project's location while their EB-5 petitions are process.
Read more about TEAs here.