What does ppm mean in mass spectrometry?

In mass spectrometry, ppm stands for parts per million. Ppm is a unit of measurement utilized to express the mass resolution or mass accuracy of the mass spectrometer. The ppm value measures the approximation error in the measured mass compared to the expected or theoretical mass. In order to calculate the ppm, one must use the formula: ppm = (theoretical m/z value - experimental m/z value / theoretical m/z value) * 10^6.