Define isotherm.

Isotherms are defined as lines that connect points of equal temperature on a weather map. These lines are crucial in meteorology because they help visualize how temperature varies across a geographic area, indicating areas of high and low temperatures. By analyzing isotherms, meteorologists can identify temperature gradients, which can be essential for understanding weather patterns and systems.

The other choices, while also relevant concepts in meteorology and geography, refer to different types of isolines. Lines of zero wind speed, for example, would indicate areas with no movement in the atmosphere, which helps in studying wind patterns. Lines of equal elevation, often referred to as contour lines, are significant in topography, showing how terrain varies. Lastly, lines of equal pressure, known as isobars, allow meteorologists to assess pressure systems and predict weather patterns such as storm fronts. Each of these concepts uses similar principles, but in this case, isotherms specifically relate to temperature.