A very wide used command line program that prints out the contents of a file on a terminal. Chances are pretty high cat is installed on your system already.

Example: If you're navigating to the folder of a git repository in your terminal and quickly want to see what the readme says without having to open a file manager or going to the website on github/gitlab/codeberg you can run:

  cat README.md
  

Which shows the text stored in that file directly in your terminal window.

bat does essentially the same, only fancier, with syntax highlighting, some formatting and colors.