The form of cocaine that can be smoked. There are three free-base forms of cocaine: coca paste made from processed coca leaves; crack (which is made with powder cocaine and sodium bicarbonate); and "free base" (which is made with powder cocaine, ammonia, and ether. This form is rarely used since crack was discovered). All free base is highly addictive.
The "free" base form of an alkaloid, i.e., not paired with an acid molecule. The free base (or freebase) form of an alkaloid can usually be vaporized and inhaled (this is called "freebasing" the drug).