n-message

A message singling out one thing from a set of $n$ is sometimes called an $n$-message. For example, a message singling out one thing from a set of 13 is a 13-message. An $n$-message carries ${\log }_2\left(n\right)$ bits of information. For a formal account of what it means for a message to "single out one thing from a set of $n$," see Information.