Toxic, or poisonous, refers to substances that can cause harm or injury to living organisms. These substances can disrupt biological processes, leading to illness or even death. Common examples of toxic materials include certain plants, chemicals, and heavy metals. Toxicity can vary widely; some substances are harmful in small amounts, while others may require larger doses to be dangerous. For instance, carbon monoxide is a colorless gas that can be lethal when inhaled, while poison ivy can cause skin irritation upon contact. Understanding toxicity is crucial for safety in both everyday life and environmental contexts.