Amarna is the modern name given to the capital city of Akhetaten (or Ahknaten), the heretic pharaoh of the 18th Egyptian dynasty, built about 1350 BC and abandoned at his death 20 years later.
First surveyed (and mapped) by Napoleon Bonaparte's 1798 expedition, Amarna was first excavated in the late 19th century, and is currently being investigated by the Egypt Exploration Society and the McDonald Institute at Cambridge. Amarna is also the name given to the period in Egypt when Akhenaten reinvented the Egyptian religion.
The best source of information is the Tour Egypt site on Amarna, and the low tech but useful Amarna Research Foundation page, making anything I'd have to say redundant.
This glossary entry is part of the Dictionary of Archaeology.
Also Known As: Tell el-Amarna, Akhetaten