Meaning:
“鸽” means “pigeon,” and “了” is a marker for perfect tense. This term, coined by Chinese netizens, derives from another colloquial saying “放鸽子” (fànggēzi, literal meaning: fly a pigeon), which actually means “to stand someone up.” Therefore, this term is used when someone fails to keep an appointment or to do something as they promised.
Example:
A: 昨天的约会怎么样？
Zuótiān de yuēhuì zěnmeyàng？
How was your date yesterday?
B: 我好不容易约到校花看电影，结果她鸽了。
Wǒ hǎobùróngyì yuēdào xiàohuā kàn diànyǐng，jiéguǒ tā gēle。
I finally got the campus belle to agree to go on a movie date with me, but she stood me up.