Asbestos is a wonderful product that served many purposes for years. It is fibrous material that acted as a stabilizer in many products and because it was fireproof it was a great insulator. Its usage was banned in specific applications in 1980 because the fibers, if inhaled, can cause asbestosis or mesythelioma -- fatal lung diseases. It is believed that just a single fiber is enough to cause disease. It is still used today but only in very limited applications.
In older housing we still find asbestos in many places including but not limited to:
floor tile manufactured before 1980
texturing on ceilings applied prior to 1980
insulation in attics and around pipes
the expansion boot in furnace plenums
This list is by no means complete and only meant to show how pervasive asbestos was at one time. The whole key to asbestos is keeping it out of the air. If you suspect asbestos do not try to remove it yourself. If the fibers are released into the air they can stay there for a very, very long time and the last thing you want is to contaminate a forced air hvac system with them. Asbestos removal is NOT a do-it-yourself job. It is best to call in a professional that is LICENSED as required by the Commonwealth of Virginia.