Definition: [Oxford Dictionary] 1. A general direction in which something is developing or changing. 2. A fashion. 3. A topic that is the subject of many posts on a social media website or application within a short period of time. （趋势；趋向；倾向；风尚；时尚；热门话题；）

Example:

This is a growing trend.

这是一个不断增长的趋势。

I confess it is a fashionable trend, but in summer, I think most people choose cotton or silk.

我承认这是个时尚趋势，但我认为大多数人夏天都会选择棉制或丝制衣物。

For more than 20 days in a row, most of the top Twitter trends were Olympics-related.

连续二十多天，推特上的大多数热门话题都与奥林匹克运动会有关。

Within minutes of the incident her name was trending on Weibo.

事件发生几分钟后她的名字就在微博上传开了。

补充说明：trending hashtags或者说a trending topic，可以指微博上的“#热门话题#”；类似的，Youtube首页上的Trending对应的中文就处理为“时下流行”。