A plane curve formed by the locus of points equidistant from a fixed line and a fixed point not on the line 抛物线到一固定直线和不在直线上某一固定点等距的点的轨迹所形成的平面曲线
2.
The locus of points in a chromaticity diagram that represents chromaticities of the radiation of planckian radiators at different temperatures 色度图中,表征不同温度下黑体辐射的色坐标的点的轨迹。