Here’s what I learned this year: Squash plants have male and female flowers. Male flowers have long stems; female have short stems, sometimes with a part resembling the mature vegetable.
If the female flower is not fertilized, sadly, no squash. The little base of the flower that resembles the squash will drop off. :(
On left: male flowers (note long stems)
On right: female Butternut Squash flower (see base of flower)