I believe it refers to a strip of the country that is strongly christian..

The following states are usually considered part of the "Bible Belt" ("*" indicating that the state is only partly in the bible belt): * Alabama * Arkansas * Florida* * Georgia * Indiana* * Iowa* * Kansas* * Kentucky * Louisiana* * Maryland* * Mississippi * Missouri* * North Carolina * Ohio* * Oklahoma * South Carolina * Tennessee * Texas* * Virginia* * West Virginia

Mostly the Southern states are referred to as the bible belt.

A Bible Belt is a typically informal term for an area in which socially conservative Christian Evangelical Protestantism is a dominant part of the culture. The term "Bible Belt" was coined by the American journalist and social commentator H.L. Mencken in the early 1920s. In particular, in the United States it is an idiom[1] for the region where the Southern Baptist Convention denomination is strongest (though many others, e. g. the Church of Christ and Assemblies of God are present, too), usually meaning the South and nearby areas. Much of the Bible Belt consists of the American South. Ironically, this region was originally colonized not for purposes of establishing a religious haven (as was the case in the Puritan colonies of New England), but for economic reasons - specifically, for the growing of cash crops such as tobacco, cotton, rice, and indigo. During the colonial period (1607-1776), the South was a stronghold of the Anglican church. Its transition into a conservative Protestant Bible Belt occurred gradually over the next century, as a series of religious revival movements, many associated with the Baptist denomination, gained great popularity in the region. Thus, the region is usually contrasted with mainstream Protestants and liberal Catholics of the northeast, the religiously diverse Midwest, the Mormon Corridor in Utah and southern Idaho, and the relatively secular western United States, where the percentage of non-religious people is the highest in the nation, reaching its maximum in the northwestern state of Washington at 27%, compared to the Bible belt state of Alabama, at only 6%.[2] Bible belts can also be found in other countries, however, including Canada, the Netherlands, Northern Ireland and some parts of Europe and Oceania (particularly the Pacific Islands). http://en.wikipedia.org/wiki/Bible_Belt