What are the street names/slang terms for Opium?
Big O, Black stuff, Block.

What is Opium?
An opioid or narcotic, made from the white liquid in the poppy plant.  
 
What does it look like?
A black or brown block of tar like substance. 

How is it used?
Smoked.

What are its short-term effects?
Opium can cause euphoria, followed by a sense of well-being and a calm drowsiness or sedation. Breathing slows, potentially to the point of unconsciousness and death with large doses. Other effects can include nausea, confusion and constipation. Use of opium with other substances that depress the central nervous system, such as alcohol, antihistamines, barbiturates, benzodiazepines, or general anesthetics, increases the risk of life-threatening respiratory depression.

What are its long-term effects?
Long-term use can lead to drug tolerance, meaning the user needs more of the drug to get similar euphorix effects.  Opium use can also lead to physical dependence and addiction.  Withdrawal symptoms can occur if long term use is reduced or stopped.

What is its federal classification?
Schedule II