The particular white a colour space, display or viewing condition treats as neutral.
Specified as a chromaticity, usually that of a CIE standard illuminant: D65 for sRGB, Display P3 and most video; D50 for print and ICC profile connection.
A white point is not a brightness setting. Two displays at the same brightness with different white points show every colour differently.
Evening 'warm' screen modes move the display's white point towards yellow.
Converting between a D65 space and a D50 workflow without adapting the white point shifts every colour slightly warm or cool.