The ender frame is an unminable block that makes up the ender portal.
Portal frames generate naturally in the ender portal found in the skyhold.
Ender Dragon's Death
In survival, if it is blown up by a creeper or TNT, the portal frame will drop itself. This means it is obtainable in survival mode without commands, and thus the player can move the ender portal to wherever they wish.
A portal frame can be activate by shift clicking on it with an eye of ender. This changes it texture to show the eye of ender inside. Once all of the portal frames are activated, the portal will open.
The portal frame cannot be moved by a piston.