ETYM Iso- + Greek baros weight.
An isogram connecting points having equal barometric pressure at a given time.
Line connecting points of same atmospheric pressure.
Line on map passing through all places with same barometric pressure.
Line drawn on maps and weather charts linking all places with the same atmospheric pressure (usually measured in millibars).
When used in weather forecasting, the distance between the isobars is an indication of the barometric gradient.
Where the isobars are close together, cyclonic weather is indicated, bringing strong winds and a depression, and where far apart anticyclonic, bringing calmer, settled conditions.