A diffuser is a device that spreads something out over a wider area.

You'll most often encounter diffusers in two contexts. An essential oil diffuser releases scented mist into the air, filling a room with fragrance instead of keeping the smell concentrated in one spot. A hair diffuser attaches to a blow dryer and spreads the hot air across a larger area, which helps people with curly hair dry their curls gently without creating frizz.

In photography, a diffuser softens harsh light by spreading it out. Photographers might place a thin white fabric between a bright lamp and their subject to create a gentler, more flattering glow. Even lampshades act as diffusers: they spread light around a room instead of letting a bare bulb shine harshly in one direction.

The key idea is always the same: taking something concentrated (whether it's scent, heat, or light) and spreading it more evenly. Think of the difference between a focused flashlight beam and the soft glow that fills a room when you turn on a ceiling light. That spreading effect is what makes something a diffuser.