Spilled or ran over the top edge of a container because it was too full.
From Old English 'oferflowan' combining 'over' (beyond) and 'flow' (move like water). The word evolved from literal water overflow to metaphorical uses describing emotions or information that exceeds normal limits.
The term perfectly captures what happens when something exceeds capacity—rivers overflow during floods, databases overflow causing computer crashes, and emotions overflow when we're overwhelmed. It's the same concept whether it's physical or abstract!
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