Good question! At first glance it seems strange that a squash would be considered a pistillate, as the squash itself is not a flower with pistils. Most plants are hermaphroditic, meaning that they are self-pollinating, containing both male and female parts. However, the squash is actually interesting in that it takes 2 flowers to produce the squash; one that is a pistillate (only pistils, no stamens), and others are staminates (only stamens).

The pistillate flowers have ovaries that sit below the pistils, and are fertilized by the staminates. Though the staminates act to fertilize the pistillates, the actual squash is derived from the pistillate ovaries, and therefore the squash fruit is considered a pistillate. Hope this helps!