What is "coffee filter"

n. filter (usually of paper) that passes the coffee and retains the coffee grounds

A coffee filter is a coffee-brewing utensil, usually made of disposable paper. This enables it to trap the coffee grounds and allow the liquid coffee to flow through.

Paper filters remove oily components called diterpenes; these organic compounds, present in unfiltered coffee are known to be antimicrobial and antiinflammatory. Metal or nylon mesh filters do not remove these components.