The term Mesoamerica—literally, "middle America" in Greek—was first used by the German ethnologist Paul Kirchhoff, who noted that similarities existed among the various pre-Columbian cultures within the region that included southern Mexico, Guatemala, Belize, El Salvador, western Honduras, and the Pacific lowlands of Nicaragua and northwestern Costa Rica. In the tradition of cultural history, the prevalent archaeological theory of the early to middle 20th century, Kirchhoff defined this zone as a culture area based on a suite of interrelated cultural similarities brought about by millennia of inter- and intra-regional interaction (i.e., diffusion).
These included sedentism, agriculture (specifically a reliance on the cultivation of maize), the use of two different calendars (a 260-day ritual calendar and a 365-day calendar based on the solar year), a base 20 (vigesimal) number system, pictographic and hieroglyphic writing systems, the practice of various forms of sacrifice, and a complex of shared ideological concepts. Mesoamerica has also been shown to be a linguistic area defined by a number of grammatical traits that have spread through the area by diffusion.
"Mesoamerica" (Wikipedia) http://en.wikipedia.org/wiki/Mesoamerica