(mathematics) A line on a scatter plot that best defines or expresses the trend shown in the plotted points. It is chosen so that the sum of the squares of the distances from the points to the line is a minimum. It also illustrates the correlation (positive, negative, or zero correlation) between the plotted variables.

(idiomatic) A clear-cut, easy to make a decision. / (law) A clearly defined rule or standard, composed of objective factors, which leaves little or no room for varying interpretation.

(basketball) An arc on the floor of a basketball court beyond which a successful shot is worth three points.

(basketball) A line parallel to the baseline, fifteen feet from the plane of the backboard, from behind which a free throw may be taken.

The distribution of data and other signals via electric power distribution wires

An imaginary line on the Earth's surface at 180° longitude, mostly through the Pacific Ocean, to the east of which the calendar date is one day earlier than to the west.

(nautical, military, obsolete) A ship of the line or battleship.

Alternative letter-case form of Mason-Dixon Line

Alternative form of Mason-Dixon Line

(historical) The boundary line between Pennsylvania and Maryland, as run (1764–1767) by Charles Mason and Jeremiah Dixon, that, before abolition, defined part of the northern boundary of states in which slavery was permitted.