'baka' originates from Japanese, specifically the written forms '馬鹿' or 'バカ', where the characters '馬' and '鹿' literally mean 'horse' and 'deer' respectively (used in a figurative story to indicate inability to tell one from the other).

'baka' appears in classical and medieval Japanese texts as '馬鹿' and was used colloquially; folk-etymology connects the compound to a Chinese anecdote about confusing a horse and a deer, and the spoken form 'baka' became widespread in modern Japanese and then entered English as a loanword.

Initially associated with the image/story of confusing a horse and a deer (implying foolishness or lack of discernment), it evolved into the general modern meaning 'fool' or 'stupid' and retains that sense in contemporary usage (including as a loanword in English).