Walls
Homescapes Guide
What are Walls in Match-3 Elements? These are tiles that surround a piece, and it prevents you from swapping that piece with the location they are blocked from. You can however, still match other pieces beside them. You just cannot move the specific piece blocked by a wall.
Power ups can be destroyed by walls most of the time, but there are some walls that cannot be destroyed so you'll need to match it with other pieces of the same color.