Magnetic lines of force are used to represent the strength and orientation of a magnetic field. Sometimes referred to as magnetic field lines, this concept provides a useful way to represent various components of the magnetic field.
According to the physics department at the University of Illinois at Urbana-Champaign, magnetic lines of force are an imaginary concept that provides a very useful way to not only represent but also to define the properties of the magnetic field being evaluated. These lines form unbroken consecutive loops centered around the positive and negative poles of a magnet. Magnetic lines of force are often used to visually represent the relative strength, area of influence and polarity of a magnetic field.