Specifically in food preparation, halal is the Islamic equivalent to the Jewish Kosher. Food that is haram, or prohibited includes pork and pork by-products, improperly slaughtered animals, and animals not killed in the name of ALLAH. Thus, Halal food is slaughtered in such a fashion as to allow the blood to completely drain out.
Halal dishes in the US most often omit beef, due to the inability to adhere to the proper slaughter techniques; but can be purchased from an approved butcher. Chicken and lamb are the most readily available halal meats.