Nodes and elements can be associated to surfaces.

When you create a mesh with the automesher, the nodes are automatically associated to the surface. When nodes are associated to a surface, you can use the Smooth panel to smooth elements on the surface and the Node Edit panel to move the nodes along the surface. Associated nodes and elements can be selected by surface, which allows you to select all the nodes and/or elements associated to a surface. Some operations break associativity. If you transform, such as translate, a surface, node, or element, associativity is broken. However, if you transform a component that contains both a surface and its associated nodes/elements, the associativity is not broken.

Associativity is also broken if you trim a surface. To re-associate a node to a surface, use the Node Edit or Project panel.
Note: Re-associating nodes to a surface is usually a time consuming task.