Marinades are used in the process of soaking foods in a seasoned, often acidic, liquid prior to cooking.  We have chicken marinades, beef marinades, fish marinades, lamb marinades to name a few. The process helps with the absorption of liquids and flavours. They are either acidic or enzymatic. In addition to these ingredients, they often contains oils, herbs, and spices to further flavour the food items. Also, you can use the marinade to baste the meat or fish whilst it is cooking to further enhance the flavour. The longer you leave protein in a marinating the deeper the flavour absorbs.