"Magnetic reversal" is the term used when the Earth's magnetic field reverses its polarity. This means that the poles flip so that the North pole becomes the South pole and vice versa. This flip takes thousands of years to complete based on computer models.
Scientists believe the Earth has undergone many magnetic reversals in its history and find no correlation between reversals and danger to human life. Scientists predict during a reversal there could be multiple poles and gradual shifting of the poles in a wandering-like pattern towards the equator. These predictions are based on mathematical models as there is currently no complete scientific record of a full magnetic reversal.