It just means that the controller lost the aircraft on the radar screen. Most likely the aircraft in question went below the controllers MVA - (Minimum Vectoring Altitude). As to why he lost him on radar, I don't know. If a plane goes down the controller will eventually lost them on radar and if i'm not mistaken, on the radio as well. I'm assuming if it was a helicopter he may have been landing but it seems like there should of been some sort of communication if that's the case. These are my assumptions.
