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Foucault found that when magnetic flux linked with a metallic conductor changes,induced currents are set up in the conductor in the form of closed loops.These currents look like eddies or whirlpools and likewise are known as eddy currents.They are also known as Foucault's currents.

Thus,eddy currents are the currents induced in a conductor,when placed in a changing magnetic field.

Through an experiment we can explain the origin of eddy currents:

                                                                        

                                                    Introduce a soft iron core inside a solenoid and connect it to a source of alternating e.m.f. Place a metallic disc over the cross sectional face of the soft iron core .As the circuit is switched on, the metallic disc is thrown up in the air. 

                 When the circuit is switched on,the current starts glowing through the solenoid.As the current grows,the magnetic field lines along the axis of the solenoid and hence the magnetic flux through the disc also increases from zero to some finite value.Due to this,induced currents are produced in the disc.According to Lenz's law, the induced current set up in the disc acts in such a manner that it opposes the increase of magnetic flux through it.As a result ,the disc is thrown up (away from the soft iron core).