When you are outside on a hot day, you might feel really sweaty and sticky. This is because there is a lot of water in the air that makes you feel damp. This water in the air is called humidity. Inside your house, there is also humidity in the air, but you probably don't notice it as much because your air conditioner helps to take some of it out.
Humidity buffering is when certain materials, like wood or plaster, can help to absorb some of the extra humidity in the air. Kind of like a sponge soaking up water, these materials can soak up some of the humidity so that your house doesn't feel too damp.
For example, if you have a room with a lot of plants, that room might feel really humid because plants release moisture into the air. But if you put a lot of wood furniture or shelves in that room, the wood can help to "buffer" some of the humidity by soaking it up. This can make the room feel less damp and more comfortable to be in.
So, humidity buffering is an important concept for making sure that indoor environments don't get too humid and uncomfortable. By using materials that can absorb some of the extra moisture in the air, we can create a more pleasant living space.