Description given to two substitutents attached to adjacent atoms when their bonds are at 180 degrees with respect to each other. Below are generic representations of anti conformations in both a Newman projection and a wedge-and-dash drawings.
This idea also explains why a carbon chain is drawn in a zig zag manner. In the zig zag conformation, all carbon-carbon bonds have the largest groups (aka the rest of the carbon chain) anti from each other. See the carbon chain below, for example.