A 2D physics engine is a software framework that simulates physical interactions in a two-dimensional space. It allows developers to create realistic movements and behaviors for objects, such as bouncing, sliding, and colliding. This is commonly used in video games and simulations to enhance realism and provide engaging experiences. These engines use mathematical models to calculate forces, velocities, and accelerations, ensuring that objects respond accurately to user inputs and environmental factors. Popular examples of 2D physics engines include Box2D and Chipmunk, which are widely utilized in game development for their efficiency and ease of integration.