Marination is the process of soaking foods in a liquid before cooking. The idea is to add flavour, and to tenderize tougher cuts of meat.
The liquid in question, the 'marinade', may be acidic (made with ingredients such as vinegar, lemon juice, or wine) or enzymatic (made with ingredients such as pineapple, papaya or kiwifruit). In addition to these ingredients, a marinade often contains oils, herbs, and spices to further flavour the food.