Are you looking for the Joomla 3 version of Snippets?
Snippets is a Joomla! administrator component (combined with a system plugin and a editor button).
With Snippets, you can create reusable snippets (pieces of text/content), and easily include them into your content via a simple tag, like:
When you edit the article (or module, or wherever you put the snippet tag), you will still see the tag. But on frontend view, you will see the content of the snippet instead.
Have a text snippet or a sentence you use often? Prepare it once, then simply insert it in articles with one click.
The great thing about Snippets is that when you change the content of a snippet, the output changes automatically in every place where you have used the tag!
Note: If instead you're looking for a solution where a certain text snippet is actually permanently inserted in the article content, you can use Content Templater instead.
With Snippets you can replace the dynamic tag with a piece of content made with the standard content editor. If you need more advanced control in your replacements you can use ReReplacer, which allows you to enter raw code, make custom plugin tags, use PHP and much more.