The term's use has evolved as more minor planets are found and studied. Some objects have shown a comet-like structure but without comet-like orbits.
The first discovered asteroids were Ceres and Pallas in 1801, with the 15th discovered in 1851, and were termed asteroids which means star-like since they appeared as points (but moved like planets). Now 100,000 have been identified, many by computer, and the estimated population is millions.
Generally, 10 meters diameter is taken as the line between asteroid and meteroid. The largest asteroids are close to 1,000 km across. Asteroids are generally classified by type of orbit and by spectrum.
Corotation Resonance (CR)
Catalina Sky Survey (CSS)
Kilometer Size Barrier
Nearby Supernova Factory (NSNF)
Palomar Transient Factory (PTF)
Wide-Field Infrared Survey Explorer (WISE)