Final answer:
A teratogen is a substance that disrupts fetal development, with alcohol being a prime example that can result in fetal alcohol spectrum disorders, causing lifelong developmental problems.
Step-by-step explanation:
The substance that interferes with fetal development and is known to cause damage to the developing embryo or fetus is called a teratogen. Common examples of teratogens include alcohol, illicit drugs like heroin and cocaine, certain prescription and over-the-counter medications, environmental toxins, and some viruses like HIV and rubella. Alcohol in particular is harmful at any level during pregnancy and can lead to fetal alcohol spectrum disorders (FASD), which can result in a variety of developmental problems such as cognitive impairment, attention deficits, and abnormal facial features. These effects are long-lasting and can continue to affect an individual into adulthood.