The woman who / that lives next door is a doctor. となりに住んでいる女性は医者だ。 Where is the cheese that / which was in the fridge? 冷蔵庫にあったチーズはどこ？ このふたつの文の who, which, that は、relative clause（関係詞節）の主語の役割をしています。

The woman who lives next door is a doctor. となりに住んでいる女性は医者だ。 who lives next door の部分を、relative clause（関係詞節）と言います。 関係詞節はそのひと、ものについての説明に使われます。 ひとに対しては、who もしくは、that を使います。 The woman that / who ...

A relative clause can be used to give additional information about a noun. They are introduced by a relative pronoun like 'that', 'which', 'who', 'whose', 'where' and 'when'. For example: I won’t ...

An essential relative clause provides necessary, defining information about the noun. On the other hand, non‐ essential relative clauses provide additional, non‐necessary information about the noun.

Relative clauses are bound clauses that modify NPs and occasionally CPs. The former are adjoined to NPs. A relative clause contains a WH-phrase which moves and is adjoined to CP: The student who likes ...