The word southeastern is an adjective. Southeastern means (1) of a region of the United States generally including Alabama; Georgia; Florida; Tennessee; South Carolina; North Carolina, (2) situated in or oriented toward the southeast.
The following articles and web pages elaborate on the word southeastern.
Located in southeastern California, 140 miles east of Los Angeles, Joshua Tree National Park includes parts of the Mohave Desert and Colorado Desert and gets its name from the spiky-tipped Joshua trees that are native to the Mohave Desert ecosystem.
Bar Harbor is a picturesque small town in southeastern Maine that is located on the northeast shore of Mount Desert Island. Nearby Acadia National Park contains Cadillac Mountain, the highest point on the eastern seaboard.
The Virginian-Pilot is the largest daily metro paper in Virginia. This newspaper serves the Hampton Roads area, the Eastern Shore of Virginia, southeastern Virginia, and part of North Carolina. It is a source for breaking news, sports information, and weather.
https://thevirginianpilot.com/
The following digital image illustrates the word southeastern.