All pumpkins are squash, but not all squash are pumpkins. They are members of a group of four distinct species, all from the genus Cucurbita (C. pepo, C. maxima, C. mixta, and C. moschata). The genus name might lead one to think that cucumbers are also included, but cucumbers, and gourds, represent different genera in the family called Cucurbitaceae. That family, of course, also includes the genus Cucurbita.
Thus ends our Wikipedia gleaning for today.