This is the 799th most frequent Chinese word.
聚
"Gather" or "assemble."
Here, '聚会' means 'to gather' or 'a gathering'. It reflects the word '聚' used in a compound verb form.
我们计划这个星期五在学校聚会。
We plan to gather at school this Friday.
In this sentence, '聚集' means 'to gather' and is used to describe accumulation or coming together, specifically of mist in this context.
秋天的早晨，湖面聚集了薄薄的雾气。
On autumn mornings, thin mist gathers over the lake.
In this expression, '聚精会神' means 'to concentrate one's attention fully', incorporating '聚' to mean focusing or concentrating.