Constructs are monster type in Diablo 4 that were added in Season 3: Season of the Construct.
What are the Constructs?
The Constructs are mechanical creatures powered by the elements and were created by Zoltan Kulle. The Constructs first appeared in Diablo 3 in Act 2 inside the Unknown Depths.
With Kulle now dead, the Constructs were left inside the Vaults and are now under the control of the evil forces of Hell.