Garnet. Credit: Mineral Information Institute.
A magnetic field can be represented by a set of lines of force (flux lines) spreading out from the poles of a magnet or running around a current-carrying conductor. These lines of forces can be seen if iron filings are sprinkled on to a sheet of paper below which a magnet is placed. The filings line up along the lines of force, the density of the lines being greatest where the field is strongest. The direction of a magnetic field is the direction a tiny magnet takes when placed in the field.
Magnetic poles are the field region in which is magnetism appears to be concentrated. If a bar magnet is suspended to swing freely in the horizontal plane, one pole will point north; this is called the north-seeking or north pole. The other pole, the south-seeking or south pole, will point south. Unlike poles attract each other; like poles repel. Earth's magnetic poles are the result of the huge "magnet" that is the Earth.
Within a magnetic field a magnetic dipole may experience a torque and a moving charge may experience a force. A magnetic field with its associated electric field is called an electromagnetic field.