The document discusses the future perfect continuous tense, which is used to describe actions that will be ongoing up until some point in the future. It provides the structure of the tense, which is subject + will + have + been + main verb + ing. Examples are given such as "I will have been working for four hours" and "She will not have been using the car." The tense is used to talk about actions that will be ongoing before some point in the future, such as "I will have been working here for ten years next week."