JSON
In plain terms
A lightweight, human-readable data-interchange format.
Going deeper
JSON represents data as key-value pairs and arrays, widely used for APIs and config because it's simple and language-agnostic. It maps cleanly to most languages' objects.
Under the hood
Text-based and ubiquitous but lacks comments and schema natively (JSON Schema adds validation).
Examples
REST API payloads, config files, NoSQL documents, JavaScript objects.
Think of it like...
Like a universally-understood packing list everyone can read and write.