object selections

[roberto2150]

Selecting multiple objects, CLICK on an object twice it is highlighted with blue heavy outline. 
What is this feature called?

[Scott Falkner · Accepted solution]

This should only happen if two or more objects are selected. It is to indicate the key object when using the align commands in the Control panel or the Align panel. It tells InDesign which object to align to. If you have multiple objects selected and click Align Top Edges then all objects will move up so the top of each object aligns with the topmost selected object, that is the objects whose top is closest to the top of the page. If you select a key object then all objects will align to that object, regardless of its position on the page. The key object will not move.