Which word signals a nonrestrictive clause in a complex sentence?

The Word "which" typically signals a nonrestrictive clause in a complex sentence. Nonrestrictive clauses provide additional information that can be omitted without changing the main meaning of the sentence. These clauses are usually set off by commas to indicate that they are not essential to the overall meaning. For example, in the sentence "The book, which I read last week, was fascinating," the clause "which I read last week" adds extra information but is not necessary for understanding the main point.