wash sale

a sale of a stock at a loss and repurchase of the same or substantially identical stock within 30 days, for which the capital loss is disallowed for tax purposes.

the simultaneous purchase and sale of large amounts of a stock or commodity by the same speculator so as to give a false appearance of wide market activity and interest in the stock or commodity.

US the illegal stock-exchange practice of buying and selling the same securities at an inflated price through a colluding broker to give the impression that the security has a strong market