What is the difference between 404 and soft 404?

Soft 404 error

Server not sending 404 error eventho it is one

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404 is a HTTP response code which means the 'Not Found'. When Server unable to find a requested resource from the client, it returns a HTTP Response code 404.

Soft 404 is when server redirects to a customised page to stop user from viewing the requested resource. There might be cases like a 404 has happened or it may not happened. The page requested is available,but that page is not working properly, So rather than ,viewing the partly wokring page, user is redirected to a custom page without providing the resource asked for.In Google’s own words: “This is like a giraffe wearing a name tag that says ‘dog’. Just because the name tag says it’s a dog, doesn’t mean it’s actually a dog. Similarly, just because a page says 404, doesn’t mean it’s returning a 404 status code.” By soft 404 means, user will be redirected to a custom page or other location because of any reasons[might be 404 or anything else.].

Source : https://stackoverflow.com/questions/42065693/difference-between-404-and-soft-404

The error 404 "page not found" means that the page you are finding server can't find he page.

Soft 404 means page not found and user will move to either home page or custom page.

Soft 404 Error these are those 404 errors when a user looks for a webpage which is not served by server and instead of this the user is redirected to the home page of that website