The Wilshire 4500 Completion Index, more commonly the Wilshire 4500, is a market capitalization-weighted index of all stocks actively traded in the United States with the exception of the stocks included in the S&P 500 index. The index is created by removing the stocks in the S&P 500 Index from the Wilshire 5000.
Additional meaning of Wilshire 4500:
Many managers of small-cap and mid-cap funds use the Wilshire 4500 as a performance benchmark. For example, Thrift Savings Plan's small-cap fund tracks the float-adjusted total return version of this index.