Market manipulation is generally understood to mean trading for purposes of effecting a price impact, not otherwise in the interest of the trader.  For example, sham sales, in which the counterparties have pooled resources, or one party takes both roles, so that transactions occur at their preferred prices, can be used to create a trap for speculators, who trade at prices not determined by market forces, but by the collusion of the manipulator(s).  The phrase is meaningful, regardless of your opinion on the moral or legal status of the act.