You can append groups of entities to your selection to speed up the process of selecting many entities from the viewport. The group can be a display group, or it can be a temporary selection group. You can click mouse button 3 on the viewport and do the following:
Create a selection group by copying entities (vertices, edges, faces, or cells) that are highlighted in the viewport into a selection group.
Append to your selected entities by pasting the entities stored in a selection group or a display group into your current selection.