ELI5 Antimicrobial Surfaces - how can a surface clean itself?

How are they and other surfaces you see around in public places considered antimicrobial without cleaning them? What does it even mean to be antimicrobial? How exactly does silver and copper kill bacteria? What did ancient civilizations do with copper?

... we explain like I'm five

Thank you to the r/explainlikeimfive community and in particular the following users whose questions and comments formed the basis of this discussion: secretantworshiper, ghosttrees, notrickwick, shinyafro and goldenslye.

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