A word used to describe someone with indistinguishable or plain features, an unrecognisable person, usually among many other people in a group. Typically this word would be used when describing each individual in a group would be impractical, for whatever reason, be it that they are too 'plain' to describe, if their identity is wanted to be kept hidden, or if their names are simply unknown. It would be common that these 'zuds' would be accompanied by someone who the beholder does know, e.g 'Ivo and his Zuds'.
More modern usage can refer to simply a collective of people, usually referred to in the third person.
Due to the connotations of large groups of young people, the word is typically associated with sinister activities.
You zuds are messing with me man