English: Newman projections of ethane conformations & their relative energy differences (not total energies). Conformations form when ethane rotates about one of its single covalent bond. Torsional/dihedral angle is shown on x-axis.

Conformations (according to IUPAC):

A: staggered

B: eclipsed

Valleys of the pink graph are conformations lowest in energy (shown as A). Peaks are conformations highest in energy (shown as B). B is highest & A lowest in energy. A is thus the most stable conformation.

Valleys are local energy minima. A can thus be classified as a rotamer (a class of conformers). Peaks are not rotamers, & are caused by repulsive forces of the hydrogens.

Source for conformation names & rotamer classification:

Pure & Appl. Chem., Vol. 68, No. 12, pp. 2193-2222, 1996.

Source for the relative energy differences & other info in this description:

McMurry JE (2003). Organic Chemistry. (8 ed.). Brooks Cole. p. 95. ISBN 9780840054449.