-w: Tells wget to “wait” or pause between requests, in this case for 2 seconds. This is not necessary, but is the considerate thing to do. It reduces the frequency of requests to the server, thus keeping the load down. If you are in a hurry to get the mirror done, you may eliminate this option.
-p: Causes wget to get all required elements for the page to load correctly. Apparently, the mirror option does not always guarantee that all images and peripheral files will be downloaded, so I add this for good measure.
--HTML-extension: All files with a non-HTML extension will be converted to have an HTML extension. This will convert any CGI, ASP or PHP generated files to HTML extensions for consistency.
--convert-links: All links are converted so they will work when you browse locally. Otherwise, relative (or absolute) links would not necessarily load the right pages, and style sheets could break as well.
-P (prefix folder): The resulting tree will be placed in this folder. This is handy for keeping different copies of the same site, or keeping a “browsable” copy separate from a mirrored copy.