Hello there,
Open University and Distance Education are similar but with a slight difference. The differences are discussed below:

Open University-
1. Open University is a university which provides the policy of open admissions, distance, and online learning programs.
2. Open University based on imparting higher education to those individuals who cannot take admissions in the traditional university.
3. It is a kind of University.
4. In an open university, there are no associated colleges and includes only study centers.

Distance Education-
1. Distance Education is a sort of learning provided by various universities to students who are not present in person at the site.
2. Distance Education was based on the purpose to allow access to education to those who are unable to attend the regular colleges.
3. It is a kind of education way.
4. In distance education, the university can either be an open university or traditional university. Therefore, various colleges affiliated to the traditional university.

Hope this information helps you.
Good luck!!