Overview
Pens (ペン, pen) are one of many writing instruments. Fountain pens, ballpoint pens, and sign pens are examples of different kind of pens.
Although universal as writing instruments, there are a wide variety of products in circulation, ranging from those specialized for specific tasks to those with some additional functionality.
External Links
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ペンとは [単語記事] - ニコニコ大百科 (NicoNico Encyclopedia)