Retired, it means that those funds that ...
... claim to follow the Russell 3000 must own stocks that are in the Russell 3000.
In other words, there are funds out there that you can invest in (i.e. through your 401K) that state that they are a mutual fund made up of stocks from companies that are in the Russell 3000 Index. They are known as Russell 3000 Index Funds. Russell 3000 Index funds have to include stocks from all companies that have been named to the Russell 3000.
If that does not answer your question, then you should find the Russell 3000 home page and research what it takes to qualify as a Russell 3000 stock.
I do believe that the Russell 3000 is made up of 3000 companies that meet the Russell 3000 criteria.
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