Three.js is a JavaScript library created by Ricardo Cabello in 2010. Nowadays, many contributors help daily to develop it on Github.
The Three.js library is often confused with WebGL ! WebGL is a “low-level” technology used to manipulate elementary 3D components such as points, lines and triangles.
Three.js uses WebGL and facilitates its integration by providing the ability to more easily manipulate complex 3D objects, lighting, shadows, and any complex element of a 3D world.
Thus, this powerful library allows to include scenes and 3D elements in web pages, thanks to the WebGL technology.