忽略不计 is a four-character verb meaning 'to disregard as negligible' or 'to ignore because it is too small or insignificant to matter.' Literally, 忽 (hū) means 'to overlook,' 略 (lüè) means 'to omit' or 'to skip,' 不 (bù) is the negation particle, and 计 (jì) means 'to count' or 'to calculate.' Together, they form an idiom expressing the deliberate decision to exclude something from consideration due to its trivial size, value, or impact.

This phrase is commonly used in formal, quantitative, or analytical contexts — especially when discussing measurements, statistics, margins of error, time intervals, or financial figures. It implies a reasoned judgment, not carelessness: the speaker acknowledges the existence of the element but deems it irrelevant for practical or logical purposes. It often appears after numerical expressions (e.g., '0.01%') or with phrases like '可忽略不计' (can be disregarded).