A definition of humans (Homo Sapiens), according to the Wall Street Journal (not available online):
Has a highly developed brain and a technological civilization. The species inhabits every continent and even low Earth orbit. Population is 6.7 billion and counting.
This reminds me of the CIA World Factbook’s capsule overview of the Earth:
Globally, the 20th century was marked by: (a) two devastating world wars; (b) the Great Depression of the 1930s; (c) the end of vast colonial empires; (d) rapid advances in science and technology, from the first airplane flight at Kitty Hawk, North Carolina (US) to the landing on the moon; (e) the Cold War between the Western alliance and the Warsaw Pact nations; (f) a sharp rise in living standards in North America, Europe, and Japan; (g) increased concerns about the environment, including loss of forests, shortages of energy and water, the decline in biological diversity, and air pollution; (h) the onset of the AIDS epidemic; and (i) the ultimate emergence of the US as the only world superpower. The planet’s population continues to explode: from 1 billion in 1820, to 2 billion in 1930, 3 billion in 1960, 4 billion in 1974, 5 billion in 1988, and 6 billion in 2000. For the 21st century, the continued exponential growth in science and technology raises both hopes (e.g., advances in medicine) and fears (e.g., development of even more lethal weapons of war).
As Jason Kottke noted about the CIA World Factbook’s entry, it seems like both of these are “meant to be read by aliens about to visit Earth for the first time.”