若有若无 as if there, but not really there
Explanation
形容事物不清晰或关系不亲密，似有似无。
Describes something unclear or a loose relationship, something that is there and yet not there.
Origin Story
小镇的集市上，一个老妇人摆摊卖一种特殊的香料。这种香料的气味若有若无，若隐若现，飘散在空气中，吸引着过往的行人。有人说闻到了淡淡的桂花香，有人说闻到了幽幽的檀香，还有人说闻到了甜甜的苹果香。老妇人只是神秘地笑着，并不解释。她只卖香料，从不透露香料的来源和制作方法。许多人慕名而来，只为一闻这若有若无的香气，感受这份神秘的魅力。老妇人家的香料，一年四季都有人来买，但却从来没有人能说清这香料到底是什么味道。
In a small town's market, an old woman set up a stall selling a special spice. The aroma of this spice was faint, sometimes present, sometimes absent, drifting in the air and attracting passersby. Some said they smelled a faint fragrance of osmanthus, others a gentle scent of sandalwood, and still others a sweet apple fragrance. The old woman simply smiled mysteriously, offering no explanation. She only sold the spice, never revealing its source or method of preparation. Many people came to her, just to smell this faint fragrance and experience its mysterious charm. People bought her spice year-round, but no one could ever clearly describe what it smelled like.
Usage
用于形容事物模糊不清，或关系不密切。
Used to describe something unclear or a not close relationship.
Examples
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他说话总是若有若无，让人难以捉摸。
tā shuōhuà zǒngshì ruò yǒu ruò wú, ràng rén nán yǐ zhuōmō
His words are always vague and elusive.
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他对我的帮助若有若无，让我心里很不踏实。
tā duì wǒ de bāngzhù ruò yǒu ruò wú, ràng wǒ xīn lǐ hěn bù tāshí
His help is so uncertain that I'm very uneasy