A thin, replaceable grip wrap applied over the permanent base grip of a racquet. Provides a fresh, tacky surface for better grip. Players go through them constantly, sometimes replacing the overgrip every few games. Nadal famously applies his overgrip with extreme precision before every match. The brand and tackiness of your overgrip is a topic recreational players have surprisingly strong opinions about.
"New overgrip at the changeover. He peels off the old one, wraps the new one, squeezes the handle. Ready to go."