Indefinite relative pronouns replace ideas that are not specific.  

They do not directly refer to a noun that has already been mentioned, as the other relative pronouns we’ve seen do (Le film que nous avons vu). 

• They can be said two ways in English: what or which. 

• Ce qui is a subject, and is always followed by a verb in the singular. 

• Ce que is an object.  The subject and verb that follow can be singular or plural, depending on the context. 

• Ce dont is the object of a verb that takes de. 

• Quoi is the object of a preposition other than de:  à, après, sur…