The ability of Immutable.js to use previous data structures to efficiently create new ones without deep cloning is referred to as ________.

The ability of Immutable.js to use previous data structures to efficiently create new ones without deep cloning is referred to as "Structural Sharing." This core concept of Immutable.js helps optimize memory usage and performance by reusing parts of the existing data structures when creating new ones. Instead of copying everything, it shares common elements, which is key to Immutable.js's efficiency and immutability.