n. 1. an imaginary line or standard by which things are measured or compared; as, they established a baseline for the budget. [ WordNet 1.5 ] 2. the back line at each end of a tennis court. [ WordNet 1.5 ] 3. (Baseball) the lines between bases on a baseball field along which a baseball player must run while running the bases. [ WordNet 1.5 ] 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. [ PJC ] 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. [ PJC ] | 