An opinion given by an Islamic
scholar. The word is Arabic
but is used by Muslims
Here's how it was explained to me: A fatwa is the opinion of a scholar about how Islamic law (Shari'a) applies to a particular situation.
Because Islam does not have a single ruling authority (other than Allah), a fatwa has as much authority as the scholar who issues it. Those who don't accept the scholar's authority won't accept the fatwa.
Devout Muslims might request a fatwa about anything from table etiquette to how to morally invest their money. This can be done over the Internet, for example at fatwa-online.com
A fatwa is not an anathema or death sentence. This misconception arose because the word "fatwa" was widely associated with an Iranian cleric's condemnation of author Salman Rushdie for writing The Satanic Verses.