Which is a photon or particle with a high enough energy to eject an electron out of its orbit when interacting with another atom, or destabilizing that atoms nucleus.
Those photons and particles can be created from other unstable nuclei that are not themselves ionizing, but can cling to the clothes skin, and then admit those ionizing particles, and you benefit from washing those off.
But technically, you're getting radiation blasted in your face from your cell phone right now. It's just not ionizing, so you don't worry about it