Semipermeability is when some things can go through a barrier, but other things cannot.
Semipermeability is like a half-open door. It means some things can get through, but not everything.
Examples:
The plastic wrap has semipermeability, so some air can get in but not all of it.
The cell membrane has semipermeability, so only certain things can pass through.
The semipermeability of the filter allows water to pass through but not the dirt.
The semipermeability of the fence means the dog can't get out, but I can still see through it.
The semipermeability of the mask lets some air in, but not all of it.
The semipermeability of the wall lets some light through, but not too much.