The Russell 2000 index is comprised of the 2,000 smallest companies in the U.S.
If you’re looking for a small cap domestic benchmark, this is a good one. Companies included in this index are reevaluated annually to make sure they can still be considered small cap companies.
Since the Russell 1000 index represents 90% of the market, the Russell 2000 index represents about 10% of the market (if you are wondering whether or not there is a Russell 3000 index, the answer is yes — it is a combination of the Russell 1000 and Russell 2000 indices).