Sulphuric acid, H2SO4, is a stong mineral (or not organic) acid. It can form any concentration in water, and at very high concentrations (>95% w/w) will spontaneously give off fumes of pure sulphuric acid. This is called fuming sulphuric acid or oleum. The old name for sulphuric acid is oil of vitriol.
Sulphuric acid has many applications, including in many chemical reactions and production precesses. In combination with nitric acid it form the nitronium ion, which is used in the nitration of compounds. The process of nitration is used to manufacture a great many explosives, including Trinitrotoluene, nitroglycerine, and gun cotton. It is also the acid used in lead-acid batteries, and so is sometimes known as battery acid.
The energy of the hydration reaction with sulphuric is highly exothermic, and if water is added to concentrated sulphuric acid it can boil. Always add the acid to the water rather than the water to the acid. Because this reaction is so exothermic, it makes it favourable in thermodynamic terms. This means that sulphuric acid is an excellent dehydration agnet, and is used to prepare many dried fruits.