Four Extinct Days (四绝日) usually fall on February 3, May 5, August 8 and November 7. There might be some +/- depending on the season (节气). These days should not be used for important personal activities or endeavours. The Qi (气) phrase is very weak or almost extinct on these days – Extinct means ‘to end’.
Activity that are undertaken on any of the Four Extinct Days will be doomed from the start and can only go down. The Four Extinct Days are not good days to use for any activity that involves growth or advancement such as marriage or important business transactions or contracts.