A zester is a kitchen utensil for removing fine shreds of zest from citrus fruit. So for an example a zester can be used the peel off the skin of a lemon or lime. Different parts of the zester can be used to make thinner or thicker peels.
Another example is in this beverage, there is a watermelon peel with carvings on the skin from a zester.
The zester was used to curl the chocolates on top of the cake. Even though the zester is primarily used on citrus fruit, it can also be used on other food items like this dessert.
In this garnish, a zester was used the carve the design that's in the turtles shell
In this dish, the zester was used to curl the carrots to top of this salad