Explainer: The Russell index reconstitution is coming up. What is it?

NEW YORK (Reuters) - Market participants are beginning to gear up preparations for the annual reconstitution by FTSE Russell of its indexes at the end of June. The event often results in the highest volume trading day of the year.Recent market volatility has heightened the likelihood for more changes than usual in this year's revamp, although FTSE Russell currently intends to move forward as planned. WHAT IS THE RECONSTITUTION?Every year, FTSE Russell reconstitutes, or refreshes, the components..