Zucchini is a squash that’s most commonly green or yellow with smooth, thin skin. It’s a summer squash, along with yellow squash, pattypan squash, crookneck squash and a few other varietals, which are at their peak during the summer months. There are even more obscure types of zucchini, such as romanesco zucchini, which has striped ridges and a different flavor, but the primary type found in your local grocery store is green zucchini squash.
There is one important note to be made about what zucchini is not. Yellow zucchini is not yellow squash. Sometimes the two are used interchangeably, but while yellow zucchini is technically a type of squash that is yellow, yellow squash is actually a different vegetable. Although they look similar, you can tell them apart by their shape: yellow squash tapers toward the neck and can sometimes have a curved neck. Yellow zucchini has a mostly uniform shape throughout, just like green zucchini.
Fun fact: The British call zucchinis courgettes.