The term 'plural possessive pronoun' refers to words that indicate possession or ownership in the plural form. The two most common examples of this type of pronoun are 'ours' and 'theirs, ' which both have four and five letters respectively. 'Ours' is used to refer to something that belongs to a group of people that includes the speaker, while 'theirs' is used to refer to something that belongs to a group of people that does not include the speaker.