A marinade is a mixture of different liquids used to season things like veggies, tofu, tempeh, meat, or fish before cooking. A marinade is used to enhance a recipe or ingredient, and add depth of flavor.
A slurry is a mixture of equal parts cornstarch to water. The water is whisked with the cornstarch to make a thickening agent. A slurry acts like roux and can be used in thickening soups, stews, sauces, and gravy.