A conducting material contains within it electric charge that is free to move.

The gray sphere shown here is a conductor that initially has no net charge.  
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When the blue ball representing a negative charge is brought near, some of the positive charge in the sphere is attracted and some of the negative charge is repelled.
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  The net rearrangment of charge in the conductor is indicated by the coloring of the sphere's surface.

When a conduting path to electrical ground is connected to the sphere on the side opposite the external negative charge, the negative charge on the sphere, repelled by the external charge, can flow off of the conductor.

Removing the conducting path and leaves the sphere with a net positive charge

When the external charge is removed, the sphere retains this net charge.

  This process is referred to as chargin by induction.