The document discusses the future perfect continuous tense, also called the future perfect progressive tense. It is used to talk about actions that will be ongoing up until a certain point in the future. Examples are provided such as "I will have been working here for ten years next week" and "He will have been travelling for 24 hours when he arrives." The tense is formed using "will have been + present participle." Its main use is to indicate the duration of an action before something happens in the future.