Wiktionary
n. (context grammar English) A pronoun in a relative clause which refers to the antecedent of the relative pronoun.
Wikipedia
A resumptive pronoun is a personal pronoun appearing in a relative clause, which restates the antecedent after a pause or interruption (such as an embedded clause, series of adjectives, or a wh-island).
1. This is the girlthat whenever it rains shecries.
Resumptive pronouns have been described as "ways of salvaging a sentence that a speaker has started without realizing that it is impossible or at least difficult to finish it grammatically". An English speaker might use a resumptive pronoun in order to prevent violations of syntactic constraints.
In many languages resumptive pronouns are necessary for a sentence to be grammatical and are required to help interpretation and performance in particular syntactic conditions.