Whenever a search engine bot request a page web server sends a status 200 which means every thing is fine but if it returns:
404: Page not found and you may come back.
410: Page not found and please do not come back or no need to come back.
Some property and classifieds listings will get indexed and they can use this 410 response status to make sure their listing no longer exists in the index and no need to come back. The property and classifieds listings expire very fast as soon as the deal closed and in those scenarios webmasters can use <meta http-equiv="expires" content="date">
If you wanna continue with the page content in a different URL you can also use the below technique to move the content permanently.
301: Search engine friendly permanent redirection i.e the page has been to moved permanently moved to a new location. This redirection can also be used if you have multiple urls to reach a single page and use canonical url to make sure if there are 2 pages with similar content you can use rel="canonical" tag in your http header to avoid duplicate url's. This would greatly help while moving the website from one domain to another or to a new location for various reasons such as to maintain theme, to address client requirements and yet search friendly.
After moving the content to a new URL using 301 and redirect the old URL to 410 instead of 404 will help to resolve lot of 404 issues in the webmaster tools where it may take a while to get rid of those URL's.