The term "minor" is used to describe the quality of a musical interval. In music theory, an interval is the difference in pitch between two notes. A minor interval is an interval that is smaller than a major interval. For example, a major third is an interval that spans three whole tones, while a minor third is an interval that spans two and a half whole tones.
Piano cords do not have a quality of sound, so they cannot be described as "minor" or "major".