Learn in the textbookExpressions, Assignment, and Comments
DefinitionA comment (注釈) is an explanation written into a program for people to read, and it is never executed.
ExplanationWriting down what a process is for or what a variable means makes the program easier to follow for whoever reads or fixes it later. IPA's pseudo-language uses forms such as enclosing the text in "/* … */" or writing it after "//". Adding or deleting comments does not change what the program produces.
AnalogyIt is like a note on a map saying "steep hill here": the road stays the same, but the note helps whoever reads the map.
Memory hookThe Japanese word combines "note" and "explain", so read it as an explanation added beside the main text.