An insulting word meaning an idiot or fool; used to belittle someone's lack of sense or intelligence.
そんなことを言うなんて、ばかじゃないの？
Saying something like that — are you an idiot?
あいつは本当にばかだと思う。
I really think he's an idiot.
人をばか呼ばわりするのはよくない。
Calling people idiots is not good.
Used adjectivally to mean stupid, foolish, or absurd (as in 'ばかな行為' — a foolish act).
ばかなミスをしてしまった。
I made a stupid mistake.
そんなばかな話は信じられない。
I can't believe such a ridiculous story.
ばかなことを言わないでください。
Please don't say silly things.
Meaning trivial or insignificant; something unimportant or disappointing.
彼の言い訳はばかに過ぎない。
His excuse is nothing but trivial.
そんなばかな理由で諦めないで。
Don't give up for such a trivial reason.
Colloquially used to say something has malfunctioned or lost sensation (e.g., 'ばかになる' — to break or go numb).
このスマホ、最近ばかになって頻繁に落ちる。
This smartphone has been acting up lately and crashes often.
長時間寒さにさらされて指先がばかになった。
After being in the cold for a long time my fingertips went numb.
Used as a slangy prefix meaning extremely or unusually (e.g., 'ばか高い' — ridiculously expensive).
この店のケーキはばか高いよ。
The cakes at this shop are ridiculously expensive.
ばか安いセール品を買った。
I bought something at an insanely cheap sale price.
Used as a slangy suffix indicating someone obsessed with or crazy about something (e.g., '釣りばか' — a person crazy about fishing).
彼は釣りばかで、週末はいつも海にいる。
He's a fishing fanatic; he's at the sea every weekend.
飲み屋では酒ばかが楽しそうに話していた。
At the bar, some booze enthusiasts were chatting happily.
The name of a species of trough shell (Mactra chinensis); a specialist/regional term.
この料理には馬鹿（ばか）という貝が入っている。
This dish contains a shellfish called 'baka' (Mactra chinensis).