This is a general counter for five unspecified items or "five pieces." It is typically used for counting various objects without a dedicated counter, for example, "five oranges" or "five wishes."

形(かたち)や種類(しゅるい)を問(と)わず、物(もの)を「五(いつ)つ」数(かぞ)えるときに使(つか)います。ミカン五(いつ)つ、願(ねが)い事(ごと)五(いつ)つなど。