Carnival denotes any atmosphere of sanctioned indulgence and illusory disorder preceding, surrounding or permeating a holiday or sacred feast. Graciously accommodated by official culture, Carnival permits the debasement of social institutions and personalities which are normally feared/respected.
The spirit of Carnival was and is one of the most powerful forces of subversion. Carnival suspends normal law and order and inverts them with parades of parody, melodramas of mockery, and festivals of farce and irreverence. Everyday reality is dismissed and denied in this world-turned-upside-down. Exaggeration and hyperbole are substituted for truth; the erotic and obscene are elevated above morality. The world of Carnival contains the marketplace, the relentless buying and selling of material goods until even human beings are reduced to mere commodities. Ultimately, Carnival is about spontaneity and the indulgence of every earthly appetite -- carnal, sexual, and aggressive.
In the middle ages, Carnival (i.e., pagan) gaiety and Christian sobriety didn't just co-exist; they were mutually incorporated to produce a religious and social occasion. Inversions and distortions of religious ritual and Christian images were standard during winter's Feast of Fools or Feast of the Innocents and other ritual spectacles in which citizens or children were permitted to "invade" the cathedral and turn it upside down and inside out. They upheld excrement on the communion chalice, led asses to the pulpit to bray sermons, and substituted obscenities and nonsense for responsorials, all at the official invitation of the clergy.
Medieval carnival players took to the streets on stilts and in masks and costumes, flaunting their various sexual persuasions very much like Americans today who take to the streets of New Orleans during Mardi Gras or those of New York for the Greenwich Village Halloween Parade. Though flamboyant and irreverent, the latter masquerades have become expressions of official culture -- sanitized and sanctified by local tourist boards. If you want to see Carnival in all its cruelty, visit 42nd Street before Disney purges it of its porno flicks, hustlers and prostitutes. Or visit a small county fair in the steamy summer where young toughs prowl for fights and cruise for chicks and sweet young things still give blowjobs to carnies for free rides on the ferris wheel.