Universal Resource Locators (URLs) are human readable strings that allow a connection on the web to be redirected to the correct IP address using ICANN's routing algorithm and its associated registry of URLs.
People share URLs everyday, however as URLs tend to be unique and consist of many components they can get quite long which can cause them to break or include unnecessary characters when being shared, especially between two applications. This is where url shorteners come in, they contain a private record of shortened urls that are one-to-one mapped to their full urls.