AFib en · NOUN Meanings (alt-of, alternative, uncountable, usually) Alternative form of A-fib alt of A-fib The most common type of irregular heartbeat is atrial fibrillation or AFib. It is estimated that between three and six million people in the United States have AFib. 2024 February 13, “Understanding Your Heart Rate”, in Emory Healthcare: Forms SpellingFeaturesLabelsSource AFibs Number=Plur lexicographic