Mirepoix

Mirepoix (pronounced /mɪər ˈpwɑː/) is the French name for a combination of onions, carrots, and celery (either common Pascal celery or celeriac). Mirepoix, either raw, roasted or sautéed with butter, is the flavor base for a wide number of dishes, such as stocks, soups, stews and sauces.

These three ingredients are commonly referred to as aromatics. Similar such combinations, both in and out of the French culinary repertoire, may include leeks, parsnips, garlic, tomatoes, shallots, mushrooms, bell peppers, chilies, and ginger. For the combination mirepoix au gras, or a Matignon, ham or pork belly are used as additional ingredients. In Cajun cuisine, a mirepoix or trinity is a combination of onions, celery and bell peppers. Wikipedia