What is HTTP 302 Redirect - Temporary Redirection

A 302 redirection is used in a website to inform the search engines that the move is only temporary, and to index the original URL instead of destination URL.

RFC 2616 explains 302 Found as "The requested resource resides temporarily under a different URI. Since the redirection might be altered on occasion, the client SHOULD continue to use the Request-URI for future requests. The temporary URI SHOULD be given by the Location field in the response. Unless the request method was HEAD, the entity of the response SHOULD contain a short hypertext note with a hyperlink to the new URI(s)."

Matt Cutts, Head of Google's webspam team discussed in his blog 'SEO advice: discussing 302 redirects' about 302 redirects. He says 302 redirect can be on-domain or off-domain.

On-domain 302 Redirect : It is simple and not prone to hijacking. On-domain 302 redirect means the 302 temporary redirection is implemented in the same domain.
For example www.example.com/ecard.asp is redirected to www.example.com/ecard/new-year-2010.asp
Off-domain 302 redirect : These are redirects from one domain to another domain that are claimed to be temporary. When a search engine receives an off-domain 302 redirect, the right thing to do is to crawl, index and return the destination page.

When 302 Redirects are used:

Special Discounts or Promotions: You would have decided to give 'Buy one Get one Free' offer to some of your products on the eve of Christmas and New Year. Here you want to display a different page with the offer for the users for certain period of time. You can use 302 temporary redirection from the original product page to its discount offer page. Once the discount period is over, the 302 redirection can be easily removed and again displays the original page. By this you will not lose your search engine credit to your page.

Redesigning of site: Some site owners decide to redesign their site at a point of time, where they have well established and highly visible in search engines. At this point of time, you never want to lose your credits from search engines. You may create a subdomain and place the site there. 302 redirect can be used from the domain to the sub-domain. This will inform the search engine that the original domain name is to be indexed and the redirection to subdomain is temporary.