1.
loser; defeated person
A person who has lost or failed, used as a derogatory label. Literally 'defeated dog.'
2.
underdog; person looked down upon
A person in a disadvantaged or inferior position, especially one who is mocked or dismissed by others.
The team that was always seen as the underdog won the championship and became big news.
負け犬 literally means "defeated dog." It is a derogatory term used to label someone as a loser or failure.
Common collocations
The proverb 負け犬の遠吠え describes someone who complains or boasts from a safe distance after losing, similar to the English expression "sour grapes." This is one of the most well-known uses of the word.
In the 2000s, the term gained a secondary usage to describe unmarried women over 30 without children, popularized by a bestselling book. This usage was controversial and is now considered outdated.