The term 'underworld' symbolizes the contrast between surface perfection and hidden decay in utopian societies like in 'The Time Machine'.
The term 'underworld' is symbolic in 'The Time Machine' in relation to the contrasting lives of the Eloi and Morlocks. The Eloi represent surface perfection but are preyed upon by the Morlocks who live underground. This symbolizes the inherent flaw in utopian societies where perfection leads to stagnation and decay.