This is the 5431st most frequent Japanese word.
あいつ
The word "あいつ" in Japanese translates to "that guy," "that person," or "that one" in English, often informal or somewhat colloquial.
The word 'あいつ' is used colloquially to denote someone familiar or slightly disdained.
あいつはいつも遅刻してくるんだよ。
He always comes late.
Here, 'あいつ' refers to a known third party in a neutral to mildly informal tone.
昨日、あいつが面白いジョークを言っていたよ。
Yesterday, he was telling a funny joke.
In this case, 'あいつ' conveys a degree of distrust or criticism when describing the person.