Why A diode has just two electrodes: the anode (the P-type side) and the cathode (the N-type side). Conventional current flows into the anode and out the cathode when the diode is forward biased; it blocks current in the reverse direction. On most diode packages the cathode is marked with a band.
Watch out Source and drain are two of the three terminals of a field effect transistor, and gate and base belong to FETs and bipolar transistors respectively, so those all describe three-terminal devices, not a diode.
Two letters, two terminals: A for Anode (current in), C for Cathode (banded end, current out).