八分 is highly polysemous because 分 can mean point, minute, cent, or one-tenth. The figurative 八分 = "eight-tenths" appears in set phrases like 八分把握 (80% confidence) and 八分像 (an 80% likeness), where it means "almost / very nearly".
history
八分 is also a calligraphic style - a Han-dynasty form of clerical script (隶书) named because the strokes are said to splay outward by 'eight tenths', i.e. with strong horizontal flair. This sense is common in art-history texts.
