So, what do you think it means? Perhaps an MOC order filling?
If I want to exit a position but can't watch the stock all day for the best exit point I can make use of a conditional order. The order is actually two or more orders where the execution of one, cancels all of the rest.
For instance. let's say I own 1000 XYZ and wish to exit the position but the stock has been trading up and down between $9.50 and $10 lately and I want to get top price. I can put in a One Cancels All order where the first order in the group is Sell 1000 XYZ Limit $9.90 and a second order of Sell 1000 XYZ MOC (Market On Close). Now, if the stock hits $9.90, the first order executes which automatically cancels the second order. If the first (Limit) order does not execute, the second automatically kicks in to sell the 1000 shares of XYZ at the Market as near to the close as possible.
Conditional orders come in many flavors and are sometimes quite useful. You should read about the different conditional orders your online broker offers.