Yes, Korean spinach is different from the common spinach sold in bunches or as baby spinach in American grocery stores. Though Korean spinach is an actual type of spinach Spinacia oleracea L., as opposed to a different leafy green vegetable entirely called "spinach" in English, it is a different cultivar/variety that has a different shaped leaf, thicker stems, and grows in cooler climates and seasons. You may be able to find the Korean spinach variety in a Korean grocery store or in other Asian markets and labeled "Korean spinach" or "Asian spinach."