LOCK

Used in the context of general equities. Make a market both ways ( bid and offer ) either on the bid, offering , or an in between price only. Locking on the offering is done to attract a seller, since the trader is willing to pay (and ask) the offering side when others only ask it. Locking on the bid side attracts buyers for similar reasons. Typically, sell side requires a plus tick to comply with short sale rules.