A magnetic field that is generated around a conductor when a current flows through it. Electromagnetic induction is also the creation of an electrical pulse in a conductor when a magnetic field moves or collapses around it.
Electromagnetic induction is the principle behind the read/write head on magnetic disks and tapes. To create (write) the bit, current is sent through a coil that creates a magnetic field which is discharged at the gap of the read/write head onto the disk platter as it spins by. To read the bit, the magnetic field of the bit "induces" an electrical charge in the head as it passes by the gap. See inductor
and wireless charging