Smudging is a way to clean and purify the air of a room or space. It is a practice that comes from Native American traditions. Usually, it involves burning a bunch of dried herbs or plants called "smudge sticks" like sage or palo santo.
To explain it like you're five years old, imagine you have a room that looks and feels yucky. It's like a big dirt pile, but invisible. When you burn a smudge stick, it's like waving a magic wand that makes the yucky dirt pile disappear. It also creates a new, fresh and clean atmosphere.