basic mistake; careless error
Casual term for a simple, avoidable mistake; often used in sports, games, or everyday situations.
I made a careless mistake in the match and lost.
こんな凡ミスをするなんて、疲れてるのかな。
Making such a basic mistake—maybe I'm tired.
A Japanese compound of 凡, “ordinary, commonplace,” and ミス, borrowed from English miss in the sense “mistake.”