front-runningnoun [ U ]
ukusSTOCK MARKETthe usually illegal act of a dealer buying shares in a company after they have had an order from a customer to buy a large number of the same shares, which is likely to have the result that the shares will go up in price. The dealer can then make a profit by selling the shares that they have bought:
Front-running is when a broker places trades for his own account before fulfilling orders previously submitted by his customer.