Dead reckoning is a method of estimating a position. It uses the last known position, speed and direction the vehicle has moved since it was at the fix, to make a good guess where the current position is.
DR can be used to overcome the limitation of GPS/GNSS technology.
GPS signal is unvailble in parking garages, tunnels. Signal is heavily degrated in urban area and near the tress as line of sight to satelite blocked or due to multipath propagation.
DR can be realized in automotive based on data from the stearing angle and wheel speed sensors.