to have one's whereabouts be unknown; to be unaccounted for; missing

(idiom) unclear or obscure; to be vague or ambiguous in speech or thought

of unknown origin; having a suspicious or dubious background

unidentified flying object (UFO); also known as [[飞碟|飛碟|fei1 die2]] or [[幽浮|幽浮|you1 fu2]]

whereabouts unknown; missing or lost

unidentified in origin; no one knows where something or someone comes from; of a dubious background

Pay no heed to merit and demerit; to fail to reward those who deserve it or punish those who deserve it.

Internet slang; used when one does not understand something but still feels it is impressive or awesome.

To not understand the situation; to be unaware of the internal details or the truth of a matter.

an object or light seen in the sky that is not readily identifiable as any known aircraft or natural phenomenon

to not understand how things work or how to behave reasonably; devoid of sense

The reason or circumstances for a death are not clearly known or identified

not to know whether one is dead or alive; status unknown

having an identity that is not known; unidentified or unrecognized

to be unclear about something or fail to comprehend its meaning

identity unknown; of undisclosed or unknown identity

to not understand something but still feel that it is very impressive or great; often used in internet contexts when someone encounters something sophisticated beyond their comprehension

not clear or definite; vague or uncertain