The word profanity is often used to denote vulgar or [salacious] words or phrases. Most [wordsmiths|people who care about precise usage], however, consider this to be incorrect. The words [obscenity], profanity and [vulgarity] are frequently used as [synonym]s. While they are very similar in meanings, they are not [identical].

The word profane is derived from the [Latin] profanus which means ‘outside the temple,’ which is to say, [unholy]. Used as a verb, to profane is to take something [holy] and to debase it. The word profanity thus denotes something which is [blasphemous] or a [sacrilege].

Obcenity refers to words or actions which are offensive to ideas of [decency] or [modesty]. Vulgarity, from the [Latin] word vulgis, meaning 'common,' implies courseness or [South Park|crudeness]. An oath (or swear), such as "God damn it!" would be profane, whereas a [scatology|scatological] or sexual crudeness would be vulgar and/or obscene. For example, "[crap]" is vulgar but mild enough that most people would not consider it obscene, whereas "[shit]" is likely closer to being an obscenity.

It is (potentially) interesting to note that it is also possible for something to be profane without being obscene or vulgar. Even [darn|mild oaths] are considered to be sacrileges by certain religious groups ([Judaism|Orthodox Jews] and [Mormon]s can be exceptionally strict on these points), so, while even the most [prude|prudish persons] would not likely consider "gosh darn it," "good heavens" or mentioning the word "God" in a conversation to be vulgar, it is profane in some circles.

Some [Southern Baptist]s (and probably members of other [Christian] groups as well) consider informal references to the deity (like "The Big Guy" or "The Man Upstairs") to be profane. Usually, profanity refers to words or actions of a nature which is specifically offensive to members of a religious group. The term blasphemy refers to a specific attack against a religious belief or group. That which is profane varies depending on the religion of the person in question.

References:
The Los Angeles Times Stylebook
Thompson, Glenda, "Hell’s Language: An Historical, Social, and Linguistical Look at Cussing" - http://www.unm.edu/~abqteach/linguistics/02-08-10.htm
...and a shout out to [Webster 1913] for nifty etymological info.

profanity (idea)