A diode is an electronics component made from a combination of a P-type and N-type semiconductor material, known as a p-n junction, with leads attached to the two ends.
These leads allow you to easily incorporate the diode into your electronic circuits.
The lead attached to the n-type semiconductor is called the cathode. Thus, the cathode is the negative side of the diode.
The positive side of the diode — that is, the lead attached to the p-type semiconductor — is called the anode.
by Dale Wilson
by Jake Hertz