noun, noun which may take the genitive case particle 'no'
redundancy; superfluity; useless addition
Refers to something unnecessary that detracts from the whole, like adding legs to a drawing of a snake. Often used in the phrase 蛇足ながら (although it may be redundant).
That explanation is redundant.
At the risk of being redundant, let me add one more thing.
From a classical Chinese story in which a man, after drawing a snake, added legs to it and lost a contest. The word literally means 'snake legs' and is used metaphorically for something unnecessary that ruins the whole.