The main groups of foods in the culinary sense are fruit, vegetables, cereal grains, nuts and seeds, meats, fish and seafood. There are also minor food groups such as herbs and spices.
However, some groups of foods (e.g. nuts or fruit) have two definitions: botanical (used mostly in a scientific context) and culinary (used in the real world when talking about food, nutrition or health). These two definitions are often confused since the botanic definition is applied frequently in the culinary sense. We are used to those culinary food groups to communicate easily in the kitchen, educational settings, restaurants, and in nutritional consultations.
This site will only consider the culinary definition, although it does provide a botanical definition in order to understand the difference.