Something; some unspecified thing or matter.
机の上に何かあるよ。
There's something on the desk.
あの映画、何か面白そうだね。
That movie looks kind of interesting.
何か飲みますか？コーヒーでもどうですか？
Would you like something to drink? How about coffee?
何か違和感を感じる。
I feel something is off.
Somehow; for some reason—used when the reason is unclear.
今日はいろいろあって、何か疲れた気分だ。
For some reason I feel tired today after everything.
何かうまくいかない気がする。
I feel like something isn't going right.
何か変だと思ったら、案の定ミスがあった。
I thought something was strange, and sure enough there was a mistake.
An interjection meaning 'So what?' or 'What do you mean?' used to challenge or ask someone to clarify.
何か？ 文句でもあるのか。
What? Do you have a complaint?
そんな言い方するなよ。何か言いたいことがあるならはっきり言え。
Don't talk like that. If you have something to say, say it clearly.