The solenoid is a long coil containing a large number of close turns of insulated copper wire. The magnetic field produced by the current carrying solenoid is similar to the magnetic field produced by a bar magnet. A solenoid is used for making electromagnets. Differences between a bar magnet and solenoid:

Bar magnet	Solenoid
It is a permanent magnet.	It is a temporary magnet. It acts as a magnet only as long as the current passes through it.
The strength of a bar magnet cannot be changed.	The strength of a solenoid can be changed by changing the number of turns in its coil or by changing the current passing through it.
The polarity (North – South) of a bar magnet cannot be changed.	The polarity of a solenoid can be changed by changing the direction of current in its coil.