One site, two domains We have a single site that we'd like to have two different domains: apply.school1.edu and apply.school2.edu.

The site is at apply.school1.edu and we'd simply like to create a domain apply.school2.edu to point to apply.school1.edu. That way we can use the domain to determine what content to load on the page.

How can we do this?
If you'd like both sites to use the same code/modules and database (thus sharing users and some content), use the domain access module at https://www.drupal.org/project/domain

If you'd like both sites to have the same code/modules but not the database, check out Multisite at 
https://www.drupal.org/docs/7/multisite/multi-site-sharing-the-same-code-base