There is a URL: http://www.thewoodgalleries.co.uk/engineered-wood/browns-engineered-wood/cipressa/ and it's been around for a while, maybe has some links, built up some authority.
Now the organization of the site is being improved and the better URL: http://www.thewoodgalleries.co.uk/engineered-wood/browns/cipressa/ is to be used for the content that is on that page.
How does the authority of the old page get to the new page? With a 301 redirect. If this is not done, when someone goes to the old URL (maybe it's linked from somewhere, maybe they have a bookmark), they get a 404 error. When Google looks at links that go to the old URL, it wants to credit the links to that page, but that page does not exist anymore as far as Google knows. Google does not know there is a new page with the same information.
For you, the page is that one post in Wordpress or wherever and that stays the same—you are just renaming it. For Google, those two URLs are different pages and in order to tell Google that the one has become the other, you need to 301 redirect it.