‘Halal’ is an Arabic word, which means lawful or allowable. Any food or drink which falls under this category is permitted for consumption.
Doubtful is otherwise known as ‘Syubhah' in Arabic. An example would be chicken that is not slaughtered according to the Islamic rituals.
'Haram' is an Arabic word, which means 'not permitted', or not allowed'. Prohibited foods include pork, intoxicants such as alcohol, and carrion.