Concessive conjunction used to acknowledge a preceding statement while introducing a contrasting or qualifying point. Often translated as 'that said' or 'having said that'.
He is young. That said, he has a lot of experience.
This plan isn't perfect. Nonetheless, it's the best we have right now.
とはいえ and かと言って both introduce a qualifying contrast after acknowledging a prior statement, but とはいえ leans more formal/written while かと言って is common in everyday speech.
とはいえ and とは言うものの both mean 'having said that,' but とは言うものの is slightly more formal and emphatic in acknowledging the prior statement.
とはいえ is a more literary 'that being said' connector, while だからと言って explicitly ties back to a stated reason before denying its expected conclusion.
From the quotative particle と, the topic particle は, and the verb 言う (to say), literally 'even if one says that'. The kana form とはいえ is standard.