It's the part of anti-Muslim sentiment in America that makes every last academic Arabist, regardless of his political leanings, cringe:* Some political commentator or politician will bemoan those Moslems who don't pray to God, but to their own special deity, Allah.
Allah. It's just the Arabic word for God.
Arabic-speaking Christians (you know, the ones being massacred in Iraq along with the Mandeans and the Yazidis?) use the word in their liturgies and Bibles, and we even have it (less commonly, but still) in Jewish texts written in Arabic. Because if you speak Arabic, when you want to say "God," you say "Allah."
If you would like to insert the word Allah into your speech in English when talking about God in an Islamic context, be sure to do it when you are talking about the practice of any other Arabic-speaking monotheist. Oh, and don't forget to say Deus when you're talking about the beliefs of Latinate Christians. That's the parallel.
It's an issue that plays out in an anti-Muslim, anti-Arab arena in American discourse; but it's also playing out conversely in Malaysia, where the courts have again upheld a law that forbids anyone but Muslims or people talking about Islamic practice from using the word Allah when they mean to refer to God.
One of the things that concerns me (as a scholar, as a feeling and thinking human being, as someone who admires an awful lot about Islam, as someone with friends and colleagues who are Muslims) is that hateful elements in this country will make hay out of that and use it as "evidence" that Muslims really do consider their God to be a whole separate deity rather than a vision of the God of Abraham that supersedes and abrogates those beliefs of Jews and Christians.
As a medievalist, it calls to mind another instance in which people took the word Allah and went to town with exetegicizing in ways that defy linguistics. This was a different case, a population of Muslims who were forced to practice and secret and did not have great access to books and teachers, namely the crypto-Muslims or Moriscos of early modern Spain.
This passage was written by an early Muslim anthropologist known to us only as the "young man from Arévalo" who recorded the customs and beliefs of his community and other crypto-Muslim ones in Spain. In this piece of his report, he distinguishes between what we recognize as the word Allah in the nominative and genitive cases (subject and object, for readers who aren't familiar with languages that decline like that) with explanations based on how he has seen them used in various contexts without really understanding the structure behind the distinctions; and so intend of identifying grammatical function as the thing that determines when one says Allah, Allahu or Allahi, he identifies other distinguishing features between the times he has heard those different terms used. It's not exactly the same thing as saying that the word Allah refers to God only in an Islamic context, but it does represent an attempt to regulate the use of the term Allah with invented frameworks and in order to distinguish oneself and one's own group from an outside group. Instead of using the Spanish word for God, he continues using the Arabic one to emphasize his hidden religion and struggles to account for how to use a term in a language he does not really know.
So, this is a public service announcement from the Middle Ages: It's a really convenient thing to latch onto when you want to make a theological point about yourself and about others, but in the end Allah just means God.
*To be fair, a good many of us are horrified by far more than just this.
** A slightly belated PSA, owing to the fact that I am basically living in a news vacuum trying to finish my book manuscript.