How to define 'serious candidate'?

[LeRaposa]

Serious means someone who is a legitimate candidate and could actually win their party's nomination. Neither Lessing nor Everson ever had any chance of winning their party's nominations and couldn't even manage to get on the debate stage. Congressman John Delaney is running for President but is not a serious candidate because he is an obscure member of Congress with zero name recognition even among Democrats. He has no chance of winning the nomination and I have no idea why he's running.

For some strange reason, every four years there are people who run for President but aren't actually interested in winning. The 2012 and 2016 Republican fields are perfect examples. In 2012 Gary Johnson, Michelle Bachmann, Ron Paul, Jon Huntsman, and Herman Cain all ran for no explainable reason. Bachmann, Johnson and Paul were fringe candidates. Jon Hunstman couldn't win because the Republican Party has not nominated a moderate since 1960. Herman Cain was running to be the joke candidate? Many people run for President to sell books (Ben Carson), others run to get a TV Show (Huckabee in '08), some run to push their pet causes (Ron Paul and Bernie Sanders), some run for the fun of it (Trump and Herman Cain), some run because they feel destined to do so (Jeb!).