Acidic describes something that contains acid or has the properties of an acid. Acids are substances that taste sour and can react strongly with other materials. Lemon juice is acidic, which is why it tastes tangy and sharp. Vinegar is acidic too, and so is the fizz in soda.

Scientists measure how acidic something is using the pH scale, which runs from 0 to 14. Numbers below 7 are acidic, 7 is neutral (like pure water), and above 7 is basic or alkaline. Battery acid rates around 1 on this scale: extremely acidic and dangerous. Orange juice sits around 3 or 4: pleasantly acidic and safe to drink.

Your stomach produces acidic digestive juices to break down food, which is why heartburn feels like burning: acidic stomach contents have splashed where they don't belong. When rain becomes too acidic from air pollution, it can damage forests and buildings. That's called acid rain.

In everyday conversation, people sometimes use acidic to describe someone's sharp, biting tone of voice or humor. An acidic remark stings like lemon juice on a paper cut.