na-adjective, noun which may take the genitive case particle 'no', noun
inexperienced; unsophisticated; green
Describes someone who is inexperienced in life in general, often with a nuance of being pure, unspoiled, or not worldly-wise. Can be used for young people or those sheltered from the world.
彼はまだうぶで、社会の厳しさを知らない。
He is still inexperienced and doesn't know the harshness of society.
うぶな新人に仕事を教えるのは大変だ。
It's tough teaching work to a green newcomer.
na-adjective, noun which may take the genitive case particle 'no', noun
Specifically refers to inexperience in romantic or sexual matters. Carries a nuance of innocence, purity, or being easily deceived in love.
彼女はうぶで、男性と話すだけで顔が赤くなる。
She is so innocent that she blushes just talking to a man.
うぶな恋愛経験
Because I only have naive romantic experience, I'm easily deceived.
純粋 means 'pure' in a broader sense (pure heart, pure substance), while うぶ specifically implies inexperience and naivety, often in social or romantic contexts.
世間知らず means 'ignorant of the world' and is more negative, implying a lack of common sense. うぶ can be more neutral or even positive, emphasizing innocence.
The origin is uncertain. It may be related to the word 初 (うぶ) meaning 'first' or 'new', suggesting a state of being unspoiled or inexperienced. The kanji forms 初心 and 生 also carry connotations of beginning and rawness.