ours和their是所有格代词。

'Ours' and 'their' are possessives.

《牛津词典》

名词所有格的，代词所有格的：名词所有格的或代词所有格的，与其有关的。

Grammar Of, relating to, or being a noun or pronoun case that indicates possession.

youdao

我穿上（我的）拉练服，走了出去。（省略人称代词的所有格）

I put on my zip suit and went out.

youdao

我穿上（我的）拉练服，走了出去。（省略人称代词的所有格）

I put on my zip suit and went out.

youdao