Short answer
It means the site is stuck in a redirect loop: address A sends the browser to B and B sends it back to A. Clear the site's cookies first, then check for conflicting https and www rules, a mismatched site URL, a security plugin or a CDN set to the wrong SSL mode. A redirect checker shows the loop.
Free tool for this
What the error means
Browsers follow redirects, but only a limited number. When two rules keep sending a visitor back and forth, the browser gives up and shows this error. It is a loop, not a missing page.
Rule out your own browser first
Open the site in a private window. If it loads, the cause is a stale cookie, so clear cookies and cache for that site. Sometimes the problem exists only for you, and that is the quickest fix there is.
Try it now: Redirect Checker →
Find the loop
Put the address into a redirect checker and read the chain. The loop shows as the same two or three addresses repeating. Which address and which status code appear tells you which rule is responsible.
The usual causes
A CDN and the server disagreeing about https. The classic is a CDN such as Cloudflare set to a flexible SSL mode while the server forces every visit to https. The CDN talks to the server over http, the server redirects to https, and the loop begins. Setting the CDN to full SSL usually ends it.
A wrong site address on WordPress. If the site and home URLs in the settings say http while the server redirects to https, or the reverse, every request bounces.
Two plugins or rules doing the same job. An SSL plugin, a caching plugin and a rule in the server file can each add a redirect. Switch them off one at a time.
A www and non-www fight. One layer sends www to non-www and another sends the reverse.
How to fix it, in order
Clear cookies. Read the chain in a redirect checker. Check the CDN's SSL mode. Check the site URL settings. Disable redirect and SSL plugins one by one. Look at the rules in the server's redirect file for duplicates.
Change one thing at a time and test after each, so you know which fix worked.
Stop it coming back
Decide on one canonical address, https and either www or non-www, and enforce it in exactly one place. Several layers all trying to enforce it is how loops start.