Sw-solutions are local energy solutions, introduced by G. Seregin and V. Sverak in 2017. "S" stands for strong/ Stokes/ split, "w" for weak. This class of solutions inherits good regularity properties from the class of strong solutions, the energy inequality and global existence from the class of weak solutions. It helps simplify the proofs of a number of important properties such as compactness, weak-strong uniqueness and persistence of singularities. Sw-solutions work well both in interior domains and near non-slip boundaries, and seem to be a natural class of solutions for the study of boundary regularity.