also: どっちも
expression
Used in affirmative sentences to mean 'both' of two items or people.
りんごとみかん、どちらも好きです。
I like both apples and oranges.
この二つの案はどちらも良いと思います。
I think both of these two proposals are good.
expression
Used with a negative predicate to mean 'neither' or 'not either'. The negative form follows later in the sentence.
どちらも正しくない。
Neither is correct.
彼はお茶とコーヒー、どちらも飲まなかった。
He didn't drink either tea or coffee.
どちらか means 'either one' or 'one of the two', while どちらも means 'both' or 'neither' depending on the sentence polarity.
Compound of どちら (which of two) + も (inclusive particle). The casual form どっちも is a contraction of どちらも.