A bit of technical background today, but something that’s worth knowing: what is a redirect?
Put simply, a redirect is an instruction on a web server to show a different web page whenever a specific one is requested. For example, you’d set up a redirect if you were removing a web page from your site but thought that it might have external links to it which you couldn’t update. In that case, you’d want anyone following those links to be taken to a page set up as a replacement.
Another possibility is that you might set up redirects if you’d changed your site’s page addresses globally, e.g. from http to https, and wanted visitors to be sent to the new version. In that case, instead of a single instruction (“if anyone asks for A, show them B”), you’d do it programmatically (“if anyone asks for a page in a particular format, change their request in a certain manner to show them a revised format”).
You’ll hear of different types of redirects: “301”, “302”, etc. I wouldn’t worry about them too much, other than to note that if you’re setting up a permanent redirect, it’s best to use a “301”, as that’s what the code stands for. Search engines will note that and update accordingly.
In most instances, if you’re removing a page from your website, you should set up a 301 redirect so that anyone following the link can get to similar content. So, for example, if you sell red, blue and yellow widgets, but are dropping red ones from your range, I’d redirect the red widgets page address to the general widgets page. This will help people who were looking for your red widgets but might be interested in a similar product, and from an SEO point of view, it might retain more ‘link equity’ from external links to the deleted page. In addition, search engines know to drop the red widgets page from their index. If you just delete the page without setting up a redirect, real visitors and search engines will both get a ‘page not found message’, which is extremely unhelpful. Real visitors may just leave and never return; search engines will keep the page in their index for a considerably longer time than you or they would want, before eventually dropping it.
In the event that you really don’t want to redirect people following a link to a deleted page, find out how to mark the deleted page with a ‘410’ code. This tells the search engines to remove the page from their index.