This is a general counter for nine unspecified items or "nine pieces." It is used when counting various objects that do not have their own specific counter suffix, such as "nine pencils" or "nine questions."

形(かたち)や種類(しゅるい)を問(と)わず、物(もの)を「九(ここの)つ」数(かぞ)えるときに使(つか)います。鉛筆(えんぴつ)九(ここの)つ、質問(しつもん)九(ここの)つなど。