A fault is a fracture or zone of weakness in the Earth's crust where rocks have moved past each other. This movement can occur due to tectonic forces, leading to earthquakes. Faults are classified into three main types: normal faults, reverse faults, and strike-slip faults, each defined by the direction of movement. Faults can vary in size, from small cracks to large systems that span hundreds of kilometers. They play a crucial role in shaping the landscape and can influence geological features such as mountains and valleys. Understanding faults is essential for assessing earthquake risks and planning safe construction practices.