Dutch loop-framed bicycle, often with a basket, no gears and a back-pedal brake — and dynamo lights! I thought that calling them “granny bikes” was a peculiarly and purely British habit, after similar constructions such as granny flat, granny gear, granny bag and perhaps granny square, but was delighted to find it translated directly.
Opoe describes a particularly aged grandmother, or old woman, a little like babushka (or indeed granny); oma is more akin to “gran” or “nan”, and you can call the same bicycle an omafiets too. A fiets (pl. fietsen) is a bike.