Wyrds are individuals with raw, untutored and very varied mental powers. In fact a significant proportion of Necromundans, maybe as high as 10% or so, have minor abilities which they don't even consider to be psychic mutations - they may be 'lucky' at cards, for example, or very good at 'guessing' what's on another person's mind, but only so that others think they were born lucky or are very perceptive rather than mutants. Wyrds have far more effective powers than this, but they are still very different from the highly trained psykers of the Adeptus Astra Telepathica. This is because Wyrds almost always develop their abilities in an undisciplined, self-taught way.