What is a Game Engine:  A game engine is software development Environment which is used developers to build Video Games. Devoloper are able to build games for Mobile devices and Consoles.

a game engine includes :

Rendering engine  for 2D or 3D graphics, a physics engine or collision detection Sound,Scripting,Animation, artificial intelligence, networking, streaming, memory management, threading, localization support, scene graph,video support for cinematic.

Some examples of Game Engines are:

Unity: is a cross-platform game engine developed by Unity Technologies, which is primarily used to develop both three-dimensional and two-dimensional video games and simulations for computers, consoles, and mobile devices.

Games made by Unity Engine: Assasins Creed Identity, Rust, Temple Run and There are many more games which were made by the unity engine.

HTML5:HTML5 is a markup language used for structuring and presenting content on the World Wide Web. It is the fifth and current major version of the HTML standard.

Games made by HTML5 :Cookie Clicker, Angry Birds, 2048 and bejeweled

OpenGL:Open Graphics Library is a cross-language, cross-platform application programming interface for rendering 2D and 3D vector graphics. The API is typically used to interact with a graphics processing unit, to achieve hardware-accelerated rendering

CRYEngine:CryEngine is a game engine designed by the German game developer Crytek. It has been used in all of their titles with the initial version being used in Far Cry, and continues to be updated to support new consoles and hardware for their games