In mathematics and physics, a coordinate singularity occurs when an apparent singularity or discontinuity occurs in one coordinate frame that can be removed by choosing a different frame.
An example is the apparent (longitudinal) singularity at the 90 degree latitude in spherical coordinates.
In fact, longitude is not uniquely defined at the poles.
This discontinuity, however, is only apparent; it is an artifact of the coordinate system chosen, which is singular at the poles.
English theoretical physicist Stephen Hawking aptly summed this up, when once asking the question, "What lies north of the North Pole?".