Dip of needle: It is downward inclination or small angle made by freely suspended magnetic needle with the horizontal.
Magnetic bearing: Magnetic bearing of a survey line is the horizontal angle between the line and magnetic meridian passing through one of its ends.
Fore bearing: Bearing of line measured in forward direction or direction of survey, is known as fore bearing.
Back bearing: Bearing of line measured in backward direction or opposite direction of survey, is known as back bearing.