Sometimes it is easier to recognize a church eligible for federal tax exemption than to describe it.
Section 501(c)(3) of the Tax Code provides exemption for entities organized and operated exclusively for “religious” purposes and does not use the word “church” at all. The Regulations define neither a religious organization nor a church. The IRS and the courts treat the issue gingerly, recognizing the deference to religious groups required by the Constitution.
Mainstream churches, synagogues, temples and mosques of traditional denominations or sects are usually easy to recognize. It is the independent entities, with less traditional beliefs, which cause most of the problems with classification.