These are *plastic tile leveling clips*, used in tile installation to ensure even spacing and a level surface between tiles. They help prevent lippage (uneven tile edges) during the setting process.
How they work:
1. Slide the clip under the tile edge.
2. Place the next tile beside it.
3. Insert a wedge (not shown here) into the clip opening.
4. After the adhesive sets, the clip is broken off and discarded.
They're essential for professional-looking tile work.