What action is taken on a radar system to clear lines?

The action taken on a radar system to clear lines is referred to as "Drop." In radar terminology, "dropping" lines typically means removing or eliminating previously drawn references or visual indicators from the radar display, often to ensure that the data presented is current and accurate. This can help prevent clutter on the screen, making it easier for operators to identify relevant information and track targets effectively.

Other terms, such as "reset" or "clear," might suggest similar actions but lack the specific context used in radar operation for referencing the elimination of lines or markers from the display. "Remove" is also a general term that does not capture the precise context of clearing lines on a radar system specifically. Therefore, "Drop" is the correct term to describe this action in the context of radar functionality.