Viscosity is a measure of a fluid's resistance to flow. It describes how thick or thin a liquid is; for example, honey has a higher viscosity than water. When a liquid has high viscosity, it flows slowly, while a liquid with low viscosity flows easily. Factors such as temperature can affect viscosity. Generally, heating a liquid decreases its viscosity, making it flow more freely. Conversely, cooling a liquid increases its viscosity, causing it to become thicker. Understanding viscosity is important in various fields, including engineering, food science, and medicine.