Quick A: a way to remove copying objects in certain case, improving performance and reducing the constraints on a class (no copy or move needed).
Recently on SO:
Copy elision is an optimization implemented by most compilers to prevent extra (potentially expensive) copies in certain situations. It makes returning by value or pass-by-value feasible in practice (restrictions apply).
It's the only form of optimization that elides (ha!) the as-if rule - copy elision can be applied even if copying/moving the object has side-effects...