The R Programming language is a specialized type of language used mostly for what is called statistical computing and also graphics.
It is a free software supported by the R Foundation. https://www.r-project.org/about.html
It is important in the AI world because AI is all about collecting and analyzing massive amounts of data.
Once data is collected data scientists want to be able to look at it and process it and they will want to use advanced mathematical techniques and models to do this.
Calculus, linear algebra and statistics are just some of the top categories of mathematics that are used in advanced data science and deep learning and machine learning.