pen pal(n = noun.person) pen-friend - a person you come to know by frequent friendly correspondence;
is a kind of correspondent, letter writer
ballpoint pen, cattle pen, cow pen, felt-tip pen, felt-tipped pen, fountain pen, holding pen, light pen, pal, pal up, pen, pen name, pen nib, pen up, pen yan, popular democratic front for the liberation of pal, quill pen, sea pen, sheep pen