The word originates from horse-racing in the United Kingdom, where an entrant in a one-horse race run under Jockey Club rules has to "walk over" the course before being awarded victory. It is the equivalent of a shoo-in in America. The Oxford English Dictionary defines it thus: "a race in which through absence of competitors the winner has merely to ‘walk over’; also in extended sense, a contest in which through the inferiority of his competitors the winner has practically no opposition. Anything accomplished with great ease".
The term is also used in competitive sports to describe the ease in which a given contest was won, for example, "the match was a walk over". It is used in regards to the ease of a victory, due to the inferiority of an opposing team/individual, rather than being indicative of a heavy defeat.
A walkover is usually the sign of a very strong mandate or unanimous support. It can however can be interpreted by critics of the faction the walkover is awarded to as a suspicious sign of electoral fraud or gerrymandering to prevent other candidates from participating. The circumstances of such an interpretation are usually controversial. Walkovers can thus often be a sign of an illiberal democracy.
However many liberal democracies in history, including the history of United States, have had uncontested elections because support for the uncontested candidate was so strong. In the United States presidential elections of 1789 and 1792, George Washington ran uncontested for President, although in the latter election the ballot for the Vice President was contested by both Federalists and Democratic-Republicans.