олени

In a sentence

• Я видел оленей в лесу.

  I saw deer in the forest.

  In this sentence, "олени" is used as the plural form of "олень" (deer) to denote the plural object seen in the forest.

• Оленьи следы были видны на снегу.

  Deer tracks were visible on the snow.

  Here, the word "оленьи" is an adjective form derived from "олени" to describe the tracks belonging to deer.

• У меня есть статуэтка оленей.

  I have a figurine of deer.

  "олени" is used here as the plural form to describe a figurine depicting multiple deer.