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depends on context… If you’re talking about ions (charged particles) valency refers to the “number of charges” (e.g. Na⁺ is monovalent whereas Ca²⁺ is bivalent). If you’re talking about binding partners, it refers to the number of binding sites – monovalent binders have a single binding site for their partner whereas multivalent (aka polyvalent) binders have more than one binding site for that binder. If you’re talking about atoms, it refers to the maximum number of bonds they can form (which is based on how many valence electrons they have) – basically how many more valence electrons do you need to get a full outer shell.