This looks like a squash plant and fruit. We cannot say what variety it is.   The volunteer grew from a seed that was inside a squash fruit that was discarded or rotted in the compost last year. The seeds from hybrid varieties produce plants that do not look exactly like the hybrid variety. It is also possible that the mystery squash is a result of a cross between two squash varieties in the same species. 

The fruit is edible and if young and tender, you may be able to prepare like a summer squash. You could allow the fruit to mature and harvest it as a winter squash once the skin hardens. It will be edible but the texture, eating quality, and storage potential is unknown. https://extension.umd.edu/resource/vegetables-not-true-type

Marian