A static uniform resource locator (URL) is a name-based website address that is direct, unchanging, clear and contains no session or user identification information. Due to their clear, direct and static nature, static URLs make better long term links and have a better clickthrough rate than redirected URLs.
Static URLs use original domain name-based addresses. The alternative to static URLs, dynamic URLs, are often created by database-driven websites that include login session tags in the URL or by URL shortening services. Dynamic URLs contain information provided by the server that delivers the content the URL points to. In many cases, the additional information in dynamic URLs makes them longer.
In the past, search engine spiders were not able to index dynamic URLs and include them in search engine results pages (SERPs). Today, Google’s Googlebot webcrawler is able to crawl dynamic URLs and convert them to static URLs. Not all search engine bots, however, are able to do so. For this reason, it's advised that webmasters use static URLs in their sitemaps. A sitemap is a list of files that search engines use to crawl a website.