An adverb meaning 'to anything' or 'in any situation' — applicable to any thing or case (similar to 何でも).
彼は何にでも興味を持つ。
He takes an interest in anything.
私は何にでも挑戦してみたい。
I want to try anything (I’m willing to take on any challenge).
何にでも理由をつけるのはやめてください。
Please stop making excuses for everything.