The "Zerg Rush" Easter egg on Google is a playful nod to the real-time strategy game StarCraft. When users search "Zerg Rush" on Google, small Os, representing the Zerg units, start falling from the top of the search results. These Os then proceed to devour the search results, and users can click on each O to eliminate them. The objective is to prevent the Os from erasing all the search results. The term "Zerg Rush" originates from the Zerg race in StarCraft, known for their overwhelming numbers, making it a fun and interactive experience for users on the Google search page.