Let $M$ be a message sent over a transmission line $T$.
Let $M$ consist of a number of codewords.
Each of the codewords comprising $M$, as it is after it has been transmitted across $T$, is referred to as a received word.
Note that if a received word $c'$ does not match its corresponding transmitted codeword $c$, then it is possible that $c'$ is not actually a codeword.