Food that's halal is allowed under the religious laws of Islam. It's especially important for observant Muslims to eat only halal meat that's been prepared in a certain way.
The adjective halal can describe non-food items, and also allowable or proper behavior. It's not considered halal for a Muslim to eat pork, for example, or to drink alcohol or use intoxicating drugs. The word halal literally means "lawful" in Arabic, and the specifics of what is and isn't halal is found in the Quran, the main religious text in Islam.