A line drawn through all points of equal atmospheric pressure along a given reference surface, such as a constant-height surface (notably mean sea level on surface charts), an isentropic surface, or the vertical plan of a synoptic cross section.

One of two or more nuclides having the same number of nucleons in their nuclei but differing in their atomic numbers and chemical properties.

1. A line connecting points of equal pressure along a given surface in a physical system.

2. A line connecting points of equal pressure on a graph plotting thermodynamic variables.