A sucker bet is a term used to describe a gambling wager in which your expected return is significantly lower than your wager(s) including:

• parlays: One bet ticket written with at least two wagers (all must win for the ticket to cash).
• teaser: A sucker wager that allows bettors to add and subtract points from posted odds.
• exotic: Any wager other than a straight bet or parlay (also referred to as a proposition or prop).

For example, the chances of correctly guessing the order of the final 3 cards of Faro

Faro (card game)

Faro, Pharaoh, or Farobank, is a late 17th century French gambling card game descendant of basset, and belongs to the lansquenet and Monte Bank family of games, in that it is played between a banker and several players winning or losing according to the cards turned up matching those already...

 is usually 1 in 6, yet the bet only pays 4:1 or 5:1. Taking insurance in Blackjack

Blackjack

Blackjack, also known as Twenty-one or Vingt-et-un , is the most widely played casino banking game in the world...

is also often considered a sucker bet.

Sucker bets are often created to lure inexperienced players into betting against large odds, blinded by the offer of "fast money" — hence the name "sucker bet".