pen - A pen is a writing instrument which applies ink to a surface. Pens may be categorized by the kind of tip on them. The main modern types are: ballpoint pens, fountain pens, rollerball pens, marker pens, Technical pens, Space Pens, and Mechanical pens. A power load that was very similar or the same as the ballpoint pen was developed by the Hungarian journalist Laszlo Biro. Biro developed a new tip consisting of a ball that was free to turn in a socket. The word used for ballpoint pens in Argentina is birome because Laszlo Biro lived there for many years; also, biro can be used to refer to a ballpoint pen in British English.