The string on the left are the wikilink or the link shorthand. tw for tiki.org, dev for dev.tiki.org, wq for wikiquote, wd for wiktionary, lq for linuxquestions, wp for wikipedia.

tw   https://tiki.org/$page
dev  https://dev.tiki.org/$page
wq   https://en.wikiquote.org/wiki/$page
wd   https://en.wiktionary.org/wiki/$page
lq   https://wiki.linuxquestions.org/wiki/$page     
wp   https://en.wikipedia.org/wiki/$page

To make a link to any external wiki or site above on this site you can use the internal wiki double round brackets syntax with a prefix as "dev:" inside. For instance, to make a link to

https://dev.tiki.org/Get-code

you could use:

((dev:Get-code))

And it would produce this link:

Get-code

It is possible to use a different string of sentence that the page name to create a more descriptive link. Following the example above we want to improve the information the visitor will see. "Get-code" is quite short, "Get-code and join Tiki dev team" is already more explicit.
you could use:

((dev:Download|Get-code and join Tiki dev team))

And it would produce this link:

Get-code and join Tiki dev team

You can do that through the link at "Admin > External wikis", that will lead you to tiki-admin_external_wikis.php:

From the same tiki-admin_external_wikis.php you can see the list of external wiki references you already introduce them and edit or delete any of them. Below you can see, as a reference, the list of external wikis that we have defined in http://doc.tiki.org :

• How to indicate and visually distinguish certain external links

• Please see flash movie of config process

• External Wiki
• ExternalWiki
• ExternalWikis