The torque settings for cylinder head bolts are the manufacturer's recommendation for how tightly the bolts holding the cylinder heads to the engine block should be fastened. This is done using a special tool called a torque wrench that measures the pressure as the bolts are tightened.
Torque, a measurement of pressure, is expressed in foot-pounds. This is calculated by multiplying a force by the distance over which it is applied. For example, 70 foot-pounds of torque is achieved by applying 70 pounds of pressure with a wrench that is 1 foot long, or by applying 35 pounds of pressure with a wrench that is 2 feet long.
Bolts that are fastened with too little pressure may not hold the components together as the manufacturer intended. Overtightened bolts can potentially bend or contribute to stress fractures and other damage in the metal of the components they are holding in place. To prevent this, the manufacturer of the engine specifies both the torque to which the bolts should be tightened as well as the order in which the bolts should be tightened. Engines are designed from different materials, have different configurations and have different specifications, so the recommended torque is different depending on the engine and the manufacturer.