Set pieces are destruction staves. The frost staff is in the Nord Style, the inferno staff is in the Dunmer Style, and the lightning staff is in the Altmer Style. These weapons are in the unobtainable tier 5 versions of their respective styles.
The set consists of destruction staves in all three types and all traits.
While the description states that 2 items are required, this is because staves are 2-handed weapons, and thus count as 2 items by themselves, so only 1 item is actually needed.