Dating sims are a video game subgenre of simulation games, usually Japanese, with romantic elements.
A framework is a set of Ren'Py script files that adds large amounts of new functionality to Ren'Py.
At the cost of having to learn the (potentially idiosyncratic) way the framework does things, using a framework lets you create new types of games with Ren'Py.
These frameworks are not part of Ren'Py proper, and are supported by their creators.
The dating sim engine provides a framework for creating dating-sim style games.