Abbreviation of 'sharp pencil' (シャープペンシル): a mechanical/propelling pencil that uses refillable leads.
授業でシャーペンを使ってもいいですか。
May I use a mechanical pencil in class?
彼はシャーペンの芯を折らないようにゆっくり書く。
He writes slowly so he doesn't break the lead in his mechanical pencil.
このシャーペンは持ちやすくて書きやすい。
This mechanical pencil is comfortable to hold and writes smoothly.