<meta http-equiv="refresh" content="0; url=https://example.com/abc.aspx">
First one is in the HTML code and the browser might not even care about it. Most do, however. They might parse the whole page first, render it and only then realize you want a redirect.
The second one is on the HTTP level. No HTML code is needed, the redirection happens anyway in any browser. Immediately on header parsing.
So the second one is the proper way to do it, uses less bandwidth and is required to be implemented by browsers.