Squash vs. zucchini

 All zucchini are squash, but not all squash are zucchini. 

 The term "squash" refers to a plant species within the gourd family, which is further divided into winter squash and summer squash. The winter types — think butternut, acorn and spaghetti squash — are physically hard, with inedible outer skins and very tough seeds. Since you can eat everything but its stem, tender zucchini falls into the summer category, as do pattypan, crookneck and zucchini's closest doppelganger, the yellow squash. 

 The resemblance between zucchini and yellow squash is the primary cause of the zucchini-vs.-squash confusion.

The easiest way to tell the two apart is color. Zucchini is generally deep green — though it can be golden yellow — while yellow squash is, well, bright yellow. Shape is another indicator. Zucchini is mainly straight, while yellow squash sports a bulbous bottom, which tapers as it gets toward the top.