Using class as type in TypeScript

Why can I use class as type in TypeScript, like word: Word in the code below?

class Dict {
  private words: Words = {};
// I wonder about this line
  add(word: Word) {
    if (!this.words[word.term]) {
      this.words[word.term] = word.def;
    }
  }
}

class Word {
  constructor(term: string, def: string) {}
}

I wanted to understand it through official document but couldn’t find related content.
https://www.typescriptlang.org/docs/handbook/2/everyday-types.html

>Solution :

You can do this in most statically typed languages. By annotating word with Word you can access its class properties.

More info:
https://www.tutorialsteacher.com/typescript/typescript-class