Final answer:
A very long essay written for a doctoral degree is called a dissertation, which involves extensive research and is defended before a committee of experts.
Step-by-step explanation:
The very long essay that students are required to write for a doctoral degree is called a dissertation. A dissertation is an extensive piece of research that a student undertakes as part of their doctoral training. In the process of working on a dissertation, students employ a variety of research methods to gather data and present their findings, typically culminating in a defense before an expert committee. The purpose of the dissertation is to demonstrate the student's capacity for critical thinking, scholarly research, and contribution to the body of knowledge in their field of study.
Writing a dissertation involves several stages, including the selection of a topic, extensive literature review, methodology design, data collection, data analysis, and writing up of the findings. It requires profound dedication and reflects the scholarly maturity of the student, as they must situate their work within the context of existing research and scholarly dialogue.