Chemical Definition:

* Proton donor: An acid is a substance that donates a proton (H+) to another substance (called a base) in a chemical reaction.

* Electron pair acceptor: Acids can also be described as electron pair acceptors, as they attract electrons from a base.

Properties:

* Taste: Acids typically taste sour (think lemon juice). Warning: Never taste an unknown substance to determine if it's an acid!

* pH: Acids have a pH value less than 7. The lower the pH, the stronger the acid.

* Reaction with bases: Acids react with bases to form salt and water.

* Reaction with metals: Some acids react with metals to produce hydrogen gas.

* Conductivity: Acids conduct electricity when dissolved in water due to the presence of ions.

Examples:

* Common acids: Hydrochloric acid (HCl), sulfuric acid (H2SO4), nitric acid (HNO3), acetic acid (CH3COOH) (found in vinegar)

* Organic acids: Citric acid (found in citrus fruits), lactic acid (found in milk), malic acid (found in apples)

Important Note: Acids can be dangerous. Strong acids are corrosive and can cause severe burns. Always handle acids with care and appropriate safety precautions.