Japanese nouns have no grammatical number, gender or article aspect. The noun "hon" () may refer to a single book or several books; "hito" () can mean "person" or "people", and "ki" () can be "tree" or "trees". Where number is important, it can be indicated by providing a quantity (often with a counter word) or (rarely) by adding a suffix, or sometimes by duplication (e.g. , "hitobito", usually written with an iteration mark as ). Words for people are usually understood as singular. Thus "Tanaka-san" usually means "Mr./Ms. Tanaka". Words that refer to people and animals can be made to indicate a group of individuals through the addition of a collective suffix (a noun suffix that indicates a group), such as "-tachi", but this is not a true plural: the meaning is closer to the English phrase "and company". A group described as "Tanaka-san-tachi" may include people not named Tanaka. Some Japanese nouns are effectively plural, such as "hitobito" "people" and "wareware" "we/us", while the word "tomodachi" "friend" is considered singular, although plural in form.