also: ゼロハン
noun
50cc motorbike
Colloquial term for a 50cc motorcycle or scooter, often used among riders. The word is usually written in kana.
ゼロ半で通学している。
I commute to school on a 50cc motorbike.
中古のゼロ半を買った。
I bought a used 50cc motorbike.
原付 is the standard legal term for a moped or motorized bicycle up to 50cc, while ゼロ半 is a casual, slangy alternative.
From ゼロ (zero) + 半 (half), referring to the 50cc engine displacement (half of 100cc).