ambiguity

The unknown integer number of cycles of the reconstructed carrier phase contained in an unbroken set of measurements.

The receiver counts the radio waves (from the satellite as it passes over the antenna) to a high degree of accuracy. However, the receiver has no information on the distance, in wavelengths, to the satellite at the time it started counting. This unknown number of wavelengths between the satellite and the antenna is the ambiguity.

Also known as integer ambiguity or integer bias.