With the release of Adobe Experience Manager 6.0, Adobe introduced a new markup language. Most of us know it as Sightly. But technically its first name was HTL, short for HTML Template Library. (Thanks to our friend Ruben Reusser who posted about the new language back in December 2013. You can watch the videos here: https://ruben42.wordpress.com/2013/12/07/ready-for-sightly-the-new-aem-templating-language/.) They mentioned that they were planning to change it from HTL to something else. That “something else” became Sightly. Some of you may have been noticing that you aren’t seeing the term Sightly as much anymore. And that is because they have changed it back to HTL. Only this time, HTL stands for HTML Template Language. If you are interested in the timing, the change seemed to take place at the end of July 2016, based on the naming update we saw in this GitHub commit.
The important thing is that functionally there is no difference between them, so if you see something on the web that calls it Sightly and one that calls it HTL, just know that they are the same. You might want to update your references to it to come in line with the new name.