The scale used to measure the acidity or basicity of a solution is called the pH scale. This logarithmic scale ranges from 0 to 14, where values below 7 indicate acidity, 7 represents neutrality, and values above 7 signify alkalinity (basicity). pH is critical in various fields, such as chemistry, biology, and environmental science, as it influences chemical reactions, biological processes, and the overall health of ecosystems.