What is an Appositive?
An appositive is a noun or pronoun directly beside another noun that explains or identifies it.
South Central Asia

Tell me about the Vietnam War.
In 1965, President Johnson sent U.S. troops to stop communist North Vietnam from captureing all of South Vietnam during the Vietnam War.
Circumference of a Circle
The cicumference of a circle equals two times pi (3.14) times the radius.
What is the second law of thermodynamics?
Often called the law of entropy, the second law of thermodynamics explains why heats flows from an area of higher temperature to an area of lower temperature.