JSON
A plain text format for structured data that apps send and receive, made of names and values.
Think of a tidy receipt with labeled lines, easy to read and total. JSON is a simple way to write data as text so two systems can understand each other.
It matters because most APIs, sets of endpoints that do tasks for your app, speak JSON. Your app sends JSON to ask for work and gets JSON back with results.
In practice JSON uses braces for objects, named sets of values, and brackets for arrays, ordered lists. The punctuation is picky, so a missing comma can break a request.