Casually or spontaneously; doing something without a clear plan (e.g., dropping into a shop, going for a stroll). Also implies suddenly or unexpectedly.
時間があったので、ふらっと駅前のカフェに入った。
I had time, so I casually popped into a café in front of the station.
休日にふらっと街を散策するのが好きだ。
I like to wander around town aimlessly on my days off.
彼は理由も言わずにふらっと姿を消した。
He disappeared suddenly without giving a reason.
仕事帰りにふらっと本屋をのぞいた。
On the way home from work I casually popped into a bookstore.