freeform assignment; open-ended project
Often refers to a school assignment where students choose their own topic, especially a long-term project during summer vacation.
For my summer vacation freeform assignment, I kept an insect observation diary.
Since you can do anything for the open-ended project, it actually makes me worry about what to choose.
宿題 is general homework, while 自由課題 is a specific open-ended project, often long-term.
自由研究 is a similar concept but emphasizes research or investigation, whereas 自由課題 can include creative works.
Compound of 自由 (freedom) and 課題 (assignment, task).