"Churches" Defined

The term church is found, but not specifically defined, in the Internal Revenue Code. With the exception of the special rules for church audits, the use of the term church also includes conventions and associations of churches as well as integrated auxiliaries of a church.

Certain characteristics are generally attributed to churches. These attributes of a church have been developed by the IRS and by court decisions. They include:

Distinct legal existence REQUIRED
Recognized creed and form of worship DONE/IN PROCESS
Definite and distinct ecclesiastical government REQUIRED
Formal code of doctrine and discipline DONE/IN PROCESS
Distinct religious history DONE
Membership not associated with any other church or denomination DONE
Organization of ordained ministers REQUIRED
Ordained ministers selected after completing prescribed courses of study N/M
Literature of its own DONE/IN PROCESS
Established places of worship REQUIRED
Regular congregations REQUIRED
Regular religious services REQUIRED
Sunday schools for the religious instruction of the young N/M
Schools for the preparation of its members N/M

The IRS generally uses a combination of these characteristics, together with other facts and circumstances, to determine whether an organization is considered a church for federal tax purposes.
http://www.irs.gov/Charities-&-Non-Profits/Churches-&-Religious-Organizations/Churches--Defined

Source: Publication 1828, Tax Guide for Churches and Religious Organizations. http://www.irs.gov/pub/irs-pdf/p1828.pdf