- a musical notation of two flats in front of a note indicating that it is to be lowered by two semitones
- Neutralisation of double impact of one-off/flat rate correction
- Neutralisation of double impact of one-off/flat-rate correction
- Barbed wire of iron or steel; twisted hoop or single flat wire, barbed or not, and loosely twisted double wire, of a kind used for fencing, of iron or steel
- Flat or profiled product used as a single skin (without insulation behind) or backed by mineral wool as part of a built up assembly (which may be a double skin).