MOOSE employs -adaptivity to automatically refine or coarsen the mesh in regions of high or low estimated solution error, respectively. The idea is to concentrate degrees of freedom (DOFs) where the error is highest, while reducing DOFs where the solution is already well-captured. This is achieved through splitting and joining elements from the original mesh based on an error Indicator. Once an error has been computed, a Marker is used to decide which elements to refine or coarsen. Mesh adaptivity can be employed in both Steady and Transient Executioners.