shortlink

 shortlink  is the use of a short-domain to create (usually with a third party link shortener service) a link that redirects to (often much) longer link, popularized on Twitter, and a subset of which are first-party permashortlinks for indieweb POSSEing and other use-cases.

Use cases
See: URL design, especially:
 * URL design: Avoid long links for reasons to use shortlinks, especially when posting places other than your own site.

Bitly
bit.ly is a third party link shortening service that has been around for a while (since when?)
 * for a long time you could use "j.mp" for bit.ly paths to shorten the link even shorter by two characters, and avoid using the restrictive .ly ccTLD.

See Others
See https://en.wikipedia.org/wiki/URL_shortening#Notable_services for a longer list that does not need to be replicated here (unless there is some IndieWeb-specific use or criticism).

Flickr
Flickr has a first-party only short domain at: that appears to redirect any non-empty paths to www.flickr.com
 * https://flic.kr/

YouTube
YouTube has a first-party (only?) short domain at:
 * https://youtu.be/

Worsens link fragility
Third party shortlinks (especially those that store the actual URL in a database and use an opaque identifier instead) have a reputation for fragility, and periodically result in a massive number of links breaking on various services that use them.

E.g. defunct 3rd party short-link services:
 * tr.im
 * twtmore
 * wl.gs