A thesis is a long piece of academic writing prepared as a part of a postgraduate level academic program which describes an original argument based on research.
Theses can be a valuable source of information, especially for topics where there are fewer published works available, but are not always appropriate resources to use for assignments which require you to find peer-reviewed literature. The references or works cited in a thesis can also be useful to find further published sources on a topic.
Visit the Finding Theses guide to learn more about where to find theses.