(at least for some folks)
This evening marks the beginning of the Islamic holy month of Ramadan or رَمَضان (ramaḍān) in the Americas and parts of Africa (elsewhere the start of the month will come a day later). Tradition holds that it was near the end of the month of Ramadan, on the “Night of Power” (لَيلة القَدر, laylat al-qadr) that Muhammad received his first revelation, the first of the series of revelations that would comprise the Qur’an (قُرآن, Qurʾān). The specific day of the Night of Power is up for debate, but almost everyone agrees that it was one of the last five odd-numbered nights of the month, with most going with the 27th as opposed to the 21st, 23rd, 25th, or 29th.
As with the beginning of all months in the Islamic calendar, the first day of the month is identified astronomically, by observance of the new moon. Visual confirmation is the only true method of determining the beginning of the month, but as astronomy has improved, so has our ability to determine in advance when the month will begin. Start days may vary by a day depending on region and observance, so Muslims in the Americas will begin the fast tomorrow, while Muslims in the rest of the world will start celebrating tomorrow evening in preparation for the first day of the fast to begin on Wednesday.
I assume most folks are familiar with the basics of Ramadan, the primary obligation of which is fasting and abstinence from worldly things (food and drink, but also tobacco and caffeine products, sexual relations, and harsh language or behavior) from sunrise to sunset. The holy month is said to begin after sunset on the day before the fast starts, since that evening is given over to celebration and preparation for the next day’s fast. It is common practice to eat two meals per day during Ramadan, a pre-dawn meal called suhoor, سُحور (suḥūr, from سَحَر, saḥar, meaning the period just before dawn), and a larger meal after sunset called iftar, إفطار (ifṭār, from the root فَطَرَ, faṭara, “to break” and having the same literal meaning as our “breakfast”). Suhoor is typically a small family meal, but iftar is often enjoyed communally, perhaps at a buffet; when I lived in the Gulf all the hotels would put out a great buffet spread after sundown every evening during Ramadan. Many Muslims break the fast by eating dates, as Muhammad is said to have done, after which they attend to the evening prayer and then enjoy the large evening meal.
The fast is required of all Muslims upon reaching puberty, so children are exempt as are the elderly, sick, and otherwise infirm. Women who are menstruating, pregnant, or breast-feeding (now I sound like a Pharma commercial) are also exempt from the fast, though they will often attempt to fast anyway (hopefully in consultation with a doctor), and it’s generally expected that any fast days they do miss should be made up after the month is over, whenever they are physically able (the same goes for those who are ill during Ramadan but later recover). Also long-distance travelers are exempt from the fast (with the expectation that they’ll make up the days they miss), but this was more an issue centuries ago, for traders on long caravan journeys, than it is today when air travel makes getting from one place to another so fast. Older children may actually try to perform the fast if they are able, because any completed fasts before they are old enough to be required to fast are essentially “banked” for them, so they’re covered if they are unable to fast in a particular year as adults.
Other Ramadan observances include lengthier prayers and Qur’an readings; many Muslims will try to read through the entire Qur’an by the end of the month. Charitable giving is also usually increased, since it is believed that good deeds performed during Ramadan count more than good deeds performed at other times of the year. Decorations may be hung in homes and public places, not unlike what we do around Christmas, but these are typically meant for children, to make the month enjoyable for them. The overall intent of the Ramadan observance is to turn one’s attention away from the things of this world and focus on the spiritual.
As far as Ramadan greetings are concerned, the two I’d stick with are رَمَضان مُبارَك (ramaḍān mubārak), “Blessed Ramadan!” and رَمَضان كَريم (ramaḍān karīm), “Generous Ramadan!”