A strong acid is the one that completely ionizes in a solution whereas, a weak acid only partially ionizes. Strong acids are corrosive in nature and cause severe burns when they come in contact with skin. But the weak acids are only mildly corrosive and are even present in our food and body.
Examples of strong acid: Hydrochloric acid and sulphuric acid
Examples of weak acid: Ethanoic acid, citric acid (present in citric fruits) and acetic acid (present in vinegar)