Pumpkin or squash
This is not an as easy a question to answer as you'd might think. Horticulturists, botanists, and philosophers have argued this for many years.
First off: There are several species of plants that are commonly called "pumpkin":
- Cucurbita pepo: These are the small fruited plants that are often referred to as pie pumpkins, and the most of the varieties run from 2 to 5 pounds; some even larger. These are the most common jack-o-lantern pumpkins, and while pretty, often produce poor quality pies. This species also includes several summer squash (such as zucchini), acorn squash, spaghetti squash, and several gourds.
- Cucurbita moschata: Most of the pumpkins in this group are the commercial pumpkins that are used for canned pumpkin products. They don't look anything like what most of us call a pumpkin, however they produce a fine-textured, dry-fleshed product. They look more like buff-colored watermelons than pumpkins. Butternut squash also fall under this species.
- Cucurbita maxima: These are the giant or mammoth pumpkins one sees at county and state fairs. Buttercup and Hubbard winter squash, as well as Turk's Turban gourds fall under this species.
- Cucurbita mixta: These are the cushaw squash. Many people prefer these for cooking because of their dry flesh and high flavor. They are also somewhat ornamental, but not as jack-o-lanterns.
The best way to answer your question is to ask one of my own: what did you plant there this year? If you didn't plant anything there this year, what was growing there last year? Or did you toss a rotting pumpkin or squash into the garden or compost pile last year? The leftover seeds could easily have germinated and produced the vine you see now. Because of the genetics of squash, the fruit and plant may look nothing like the parent it came from.
Whatever that is: it's definitely a type of winter squash/pumpkin. It is definitely edible, although I can't make any guarantees at how good it will taste. I'd suggest letting the fruit ripen and see what happens.