The structure shown is cyclohexane (unsubstituted) with the axial hydrogens on one side of the ring highlighted, to emphasize how close they are in space. The steric interaction between these groups is called the 1,3-diaxial interaction, since the groups are on the 1 and 3 carbons. Due to these 1,3-diaxial interactions, groups larger than hydrogen prefer the less sterically hindered equatorial positions.