A subset of a normed space, or a topological vector space, which is closed, convex, absorbing, and balanced. A topological vector space is said to be barrelled if every barrel contains a neighbourhood of the origin.
Chemistry
A measurement of volume, widely used in the chemical industry, equal to 35 UK gallons (approximately 159 litres).
Chemical Engineering
A unit of volume used largely in the oil industry. In the US, one barrel is equal to 42 (US) gallons and equivalent to 0.158 98 m3. One barrel (British) is equal to 36 Imperial gallons and equivalent to 0.163 659 m3. The abbreviation is bbl. An oil refinery production and throughput is often quoted in terms of barrels per calendar day (BPCD) or barrels per stream day (BPSD), which are the average rates based on a 365-day year, or on the number of days per year the refinery was actually operating, respectively.
Geology and Earth Sciences
A unit of volume used to measure dry goods or liquids. An oil barrel (bbl) is equal to 42 US gallons = 34.9723 imp. gallons = 158.983 litres = 0.159 m3.