1.An imaginary line or standard by which things are measured or compared; as, they established a baseline for the budget.
2.The back line at each end of a tennis court.
3.(Baseball) The lines between bases on a baseball field along which a baseball player must run while running the bases.
4.A measurement that represents the value of a physical quantity (such as a voltage, or a level of radioactivity) in the absence of effects from other variables in a measurement, test or experiment; a control value.
5.Any horizontal line in a plot, graph, or diagram, or on a visual display in an electronic device, used as a reference point to which other values are referred.
