A groundstroke hit while moving forward toward the net, used to set up a volley or overhead on the next shot. The idea is to hit a deep, forcing shot that puts your opponent on the defensive, then close in at the net to finish the point. Shot selection matters here: a weak approach shot is basically an invitation for a passing shot winner.
"Deep slice approach shot down the line, then she closes to the net for the volley. Textbook construction."