Hello Ashish,

Hope the answer till now you received had clear you point much, just to provide you more info on your doubt I had written 2 article on FindNerd you can take reference from there: one is on "Soft" 404 Error and the second one is HTTP Status Codes and its Impact on SEO .

The reason is very clear and easy "Why HTTP 404 Status code is different from "Soft 404"?

404 status code come when user request for the page and the server couldn't find it and returns 404 not found error. It clearly provides the message to the search engine that page doesn't exists hence the search engine will not crawl the content of that particular page.

Whereas Soft 404 Status Code is the code which comes when the user requested for the page which doesn't exists or server was unable to find what was requested so instead of showing the 404 Error Message to the user server will redirect or return him to the another page.
Hence this will creates a positive feeling within the mind of end user that his actual search end with a result which is highly related to the query which he/she was searching for. And as a result of which user still engaged with the website.

Such practices are generally used when the page is under maintenance and the client do not want to lose their user to leave the website.

Yes, there is a between 404 and Soft 404 Error.
 404 Errors: Are  those errors when a user search for a webpage and the server can’t find it to serve the user. 
Whereas,
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 re-directed to the home page of that website.
Hope this was of Help 

There are difference between 404 and Soft 404 Error

The error 404 mean “page not found” that means the page you are finding server can't find the page.
Soft 404 means page not found and user will move to either home page or custom page.it simply means redirect the page to another page.

404 Error and Soft 404 error both are different how! check out below

404 Error

When we see the HTTP 404 Not Found Error means that the web page you were trying to reach could not be found on the server. It is a Client-side Error which means that either the page has been removed or moved and the URL was not changed accordingly, or that you typed in the URL incorrectly.

Soft 404 Error

 Usually, when someone requests a page that doesn’t exist, a server will return a 404  error. This HTTP response code clearly tells both browsers and search engines that the page doesn’t exist. As a result, the content of the page  won’t be crawled or indexed by search engines.
Also, you can check complete details here- https://support.google.com/webmasters/answer/181708?hl=en

Hi Ashish,
Interesting question, yes, there is difference between 404 & soft 404 and there is a little bit difference in it.

404 page not found error, means the server is not able to find the page you are looking for, while soft 404 error, means that the server redirects you to the home page or the custom page, if it doesn't find the page, you are looking for.  

Yes there are other 404 errors too. They are-
404 Bad Request - When server is unable to understand the client's request then a 404 Bad Request page appears.
 
404 -File or Directory Not Found page -  This page appears when-
 1. Server is Down
 2. No Internet Connection/ Internet connection is Down
 3. Broken Links
 4. Incorrect URL's