What is field lines? What is …

(a) Magnetic field:
The magnetic field is the area around a magnet in which there is magnetic force. Moving electric charges can make magnetic fields. In physics, the magnetic field is a field that passes through space and which makes a magnetic force move electric charges and magnetic dipoles.
(b) Magnetic lines around bar magnet:

This is the respective diagram of a bar magnet with magnetic field lines.
The lines originate from the north pole and terminate on the south pole of the bar magnet.
The magnetic field lines make closed loops.
(c) Characteristics of magnetic field lines:

• The lines originate from the north pole and terminate on the south pole of the bar magnet.
• The strength of the magnetic field is proportional to the density of lines.
• Magnetic field lines cannot cross each other.
• Magnetic field lines are continuous loops.