"Hey!" is an interjection.

hey 是个感叹词

This is a new interjection from the US that seems to have inveigled its way into common speech over here.

这个来自美国的感叹词似乎已经以诱骗的方式进入了我们这里的日常用语。

Fail—"a noun or interjection used when something is egregiously unsuccessful"—was 2009's the most useful word.

失败——“名词或感叹词，当某事非常不成功时使用”——被评为2009年最有用的单词。

The OED defines LOL as an interjection "used chiefly in electronic communications… to draw attention to a joke or humorous statement, or to express amusement".

《牛津英语词典》将 LOL 定义为一个叹词，“主要用于电子通信……以引起对笑话和幽默语句的注意，或表示可笑”。

The bishop was prepared for this interjection.

主教对这一插话是有思想准备的。

This 'ah' is an interjection used to express surprise.

啊：语气上扬，表示惊讶。