What part of speech is noun?

Noun is a word class, also known as a part of speech. It's not a part of speech itself, but rather a category that encompasses words that represent:

* People: teacher, friend, child

* Places: school, park, city

* Things: book, table, phone

* Ideas: love, happiness, freedom

So, while "noun" isn't a part of speech, it's the term used to describe the category of words that represent those things.