What's A Presentation With A Beamer?

Hey everyone, beginner to R. Recently, R Markdown exposed me to presentations with beamers. What exactly is a presentation with a beamer? I have heard of PowerPoint slides, Google Slides, but never a presentation with a beamer? Also, please explain in very simple terms if possible. Thank you.

"Beamer" is the name of a program, not a thing. LaTeX is a software system for typesetting documents. It is particularly useful when writing documents that contain mathematics. Beamer is a program for creating slideshows written using LaTeX. It is somewhat similar to PowerPoint and other presentation programs, but uses LaTeX to generate PDF files containing the presentations. It does not have a WYSIWYG editor of its own, although I believe there are some open-source WYSIWYG Beamer editors out there.

Instead of using a graphical interface like PowerPoint or Google Slides, you write the content of your presentation in a plain text file using LaTeX commands.
You compile this text file to produce a PDF file, which contains your slides.

As @prubin and @StephenSaint have explained, Beamer produces a pdf file containing slides. What's important in this context is that RMarkdown will produce a basic Beamer presentation without you having to know any LaTeX.