A comment is some text that is included in a program for the sake of human readers, and that is not really part of the program.
Comments can explain what the program does, and how it works.
Nearly all programming languages have provisions for comments, because programs are typically hard to understand without them. The Octave interpreter ignores the rest of a line following a sharp sign or percent symbol. This means that users of Octave can use the same commands to get help for built-in functions, and for functions that you have defined.