Why CW stands for "continuous wave," the oldest amateur mode, in which an unmodulated carrier is switched on and off in the dot-and-dash patterns of Morse code. The FCC emission designator is A1A, and because the signal occupies only a very narrow bandwidth (roughly 100-150 Hz) it gets through noise and weak-signal conditions well. In casual amateur usage, saying "CW" and saying "Morse code" mean the same thing.
Watch out Error correction using code words describes forward error correction schemes in digital modes, and CW has no built-in error correction; the operator's ear does the decoding. Nothing about CW involves a propagation mechanism.
CW = Continuous Wave keyed on and off = Morse. Think "carrier, wiggled" by a straight key.