What does UO mean in Unclassified?

Uh oh

Uh-oh (British English, American English ) is a ubiquitous interjection or expression of dismay in the English language, usually said in anticipation of something bad about to happen, with the sly admittance of guilt that one may have caused something bad to happen, or perceiving that something bad has already happened. The speaker often gives vent to the expression immediately upon learning or perceiving of something that presages disaster. It is an expression usually acquired very early in life, typically as early as the toddler stage. It is one of only a few words or phrases in American English commonly pronounced with a glottal stop.

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