What makes a show a "hit"?

I take a backseat to no one in my Joss Whedon fandom and I'm thrilled to see that the PGA is giving him an award. But does this make sense?

Whedon is a producer, writer, director, and creator for such hit television programs as “Buffy the Vampire Slayer,” “Angel,” “Firefly,” and “Dollhouse.”

Firefly and Dollhouse ran for a combined two seasons! It says nothing about the quality of the product to note that these are definitively not hits.