fold ‧ er /ˈfəʊldə $ ˈfoʊldər/ BrE AmE noun [countable]
[ Word Family: verb : ↑ fold , ↑ unfold ; noun : ↑ fold , ↑ folder ; adjective : folded, ↑ folding ]
1 . a container for keeping loose papers in, made of folded card or plastic
2 . a group of related documents that you store together on a computer