Relish is a
vegetable condiment often made from
pickles.
Other bases from which to make relish include onion, cranberry, zucchini, beet, cabbage, avocado, pear, corn, garlic and tomato.
Relish is generally made from a pickled vegetable that is combined with spices. The ingredients list on the jar of sweet pickle relish in my fridge includes cured cucumbers, vinegar, salt, spice and dehydrated bell peppers. It also includes artificial coloring, so I think I'll stop buying that brand.
Other varieties and different forms include chutney, raita, sambal, achar, kimchi, piccalilli and chow chow.