* Universities that merged with other institutions: Many smaller colleges and universities have merged with larger ones over time. The original names often disappear, but the history might be preserved within the archive of the successor institution. Specific examples are difficult to cite without knowing a region or time period.
* Universities that closed permanently: Reasons for closure include financial difficulties, declining enrollment, loss of accreditation, or changes in societal needs. Again, specific examples are numerous and regionally specific. Researching defunct universities in a particular geographic area (e.g., "defunct universities in Scotland") will yield more relevant results.
* Universities that changed their name and/or status: A university might significantly alter its structure, leading to a functional end to the original institution even if it continues under a different name or as a different type of educational establishment (e.g., a college).
* Universities that were destroyed during wartime or other disasters: War and natural disasters have led to the destruction of buildings and the disruption of educational activities, effectively ending some universities.
To find information about a specific defunct university, you'll need to know its name and location and search online using those terms. Academic archives, historical societies, and local libraries are good resources for this type of research.