jq is a tool that can query (search/extract/format) JSON (JavaScript readable data files).

I figured from the README that TUI probably stands for Text User Interface as it seems to support keystrokes in a way that an editor like Vi or Emacs work in a terminal (yeah I hadn't of it either, but I guess it is a retro acronym from GUI which is more well known)

And 'playground' often refers to interactive code environments, like this one for trying out tree-sitter parsing:

https://tree-sitter.github.io/tree-sitter/playground

TUI is anything sorta graphical and interactive in a terminal. Often but not always ncurses stuff.