All are squash. For convenience squashes are subdivided into two divisions. Summer squash are used as immature fruits and winter squash which are used as mature fruits. A few varieties can be used either way. Summer squash are further divided into crooknecks, straight necks, zucchini and scallops. Zucchini comes in many shapes and colrors, but they are all squash. Most summer squash are in the species C. pepo. Winter squash may be C.pepo, C.maxima, C. mixta or C. moschata.
Some zucchini photos. {{gwi:74215}} {{gwi:35947}} {{gwi:68683}} {{gwi:74216}} {{gwi:74217}} {{gwi:74218}} {{gwi:74219}} {{gwi:70533}}

In scientific terms, the squashes are all in the genus Cucurbita. This category means that all species in this genus share common traits, like the notorious vining habit, orange/yellow star shaped flowers; they also differ in certain traits based on the species and subspecies chosen, like fruit size and color, length of storage time, and plant size.

Zucchini, yellow/summer squash, typical pumpkins are all Cucurbita pepo, which are mostly squashes you grow to eat young or not store long. Cucurbita maxima has many hard winter squashes. A combo of winter and summer squashes is Cucurbita moschata.

When I talk about the plants as a general group, I call them "squashes" or "cucurbits" (as interchangeable terms), and then I refer to the specific species/subspecies by their names "zucchini" or "pumpkin" or "acorn squash", you get the idea. Most of these genus are native to Central America and are an awesome example of natural selection and speciation.

I attached a link to the Wikipedia page where you can read more about Cucurbita!

Here is a link that might be useful: Cucurbita

Thank you very much.

Hows it go? All zucchini are squash but not all squash are zucchini...

Isn't it the same thing for pumpkins? All pumpkins are squash but not all squash are pumpkins. A friend of mine wont let me call winter squash a squash. She calls them all pumpkins, what ever color shape or form.