An Acid ( from the Latin word acidus meaning sour) is considered any chemical compound that, when dissolved in water, gives a solution with a hydrogen ion activity greater than in pure water IE: a pH level less than 7.0  Examples: Acetic Acid (in Vinegar) and Sulfuric Acid used in Car Batteries. Do not mess with Ca Batteries if you get it on your skin it will burn little holes in you and if you get it on your clothes it will do the same.The different kinds of Acids are: Hydrochloric Acid: This is a solution of Hydrogen Chloride dissolved in water. The PH level is 2. The next Acid on my list is: Sulphuric Acid: This solution of sulphur Trioxide in water. Do not try to dissolve crystals of sulphur Trioxide in water as it is very dangerous. The PH level is 0.3. Ethanoic Acid or as most people know it as Acetic Acid you can find it in some of  your food for example: Grapes, and in wine which grapes are in some wine. The PH level for Acetic Acid is 3. The last Acid on my list is: Carbonic Acid: which is food in most of all the sodas made some favored waters have Carbonic Acid in them. The PH level for Carbonic Acid is 3. Also i have Uploaded a few videos on different Acids.