Minecraft Wiki
Not to be confused with Mojang.

Molang is a simple expression-based language designed for fast, data-driven calculation of values at run-time, and with a direct connection to in-game values and systems. It is used in Bedrock Edition's Add-on system with its purpose being enabling low-level systems like animation to support flexible data-driven behavior for both internal and external creators, while staying highly performant. [1]

Mojang provides official documentation Molang Documentation which goes into details of how the language works and where it's used.