i.e. Not wilfully, designedly, or maliciously, but inconsiderately, through mistake, or indiscretion, or carelessness. See Leviticus 4:2.
Related Commentaries of Numbers 35:11
Numbers 35:11
11 Then ye shall appoint you cities to be cities of refuge for you; that the slayer may flee thither, which killeth any person at unawares.