used to refer to a single person when you do not know who they are or when it is not important who they are

There's someone outside the house. 屋子外面有人。

Someone must have seen what happened. 肯定有人看见了所发生的一切。

Eventually someone in the audience spoke. 观众里终于有人开口说话了。

You'll have to ask someone else. 你得问问别人。

We'll need a software engineer or someone (= a person with skill of or like the stated type) on the project team. 我们的项目组中需要有个软件工程师之类的人。