Halal is easily associated with food, though is a wider idea applying to everyday life -- you could take it as a rough translation of a word like "ethical".
When applied to food, it most significantly means no pork, but also relevant are means of death, source (e.g no carrion), and processing. Slaughter should be done by a Muslim - mostly because it is certain that the basic rules are adhered to. Depending a little on which parts of Islam(verify) and on strictness of adherence, it potentially includes any "food of the people of the book", which easily includes the other Abrahamic religions, Christians and Jews.
Compare with Kosher