An isobar is a line on a weather map connecting places that have the same air pressure at the same time. Think of air pressure as the weight of all the air above you pushing down: sometimes there's more air pressing down (high pressure), sometimes less (low pressure). Meteorologists measure this pressure and draw isobar lines to show patterns, much like how a topographic map uses lines to show elevation.

On a weather map, isobars look like wavy or curved lines, often forming circles or ovals around areas of high or low pressure. When isobars are close together, it means the pressure is changing rapidly over a short distance, which usually signals strong winds. When they're spread far apart, the winds tend to be calm.

Weather forecasters study isobar patterns to predict storms, wind speed, and general weather conditions. If you see a weather map with lots of tightly packed isobars spiraling inward, you might be looking at a developing storm system.

In a completely different scientific context, isobars are atoms of different elements that have the same total mass number in their nuclei but different numbers of protons. But when you hear someone mention isobars, they're almost always talking about weather maps in everyday conversation.