Acoustic Glossary

Quality Factor Definition (IEC 801-24-12) a measure of sharpness of resonance of a system, being 2π times the ratio of the maximum stored energy to the energy dissipated during one cycle
Note : historically, the letter Q was an arbitrarily chosen symbol to designate the ratio of reactance to resistance of a circuit element. The name "quality factor" was introduced later

Quantity Symbol Definition (IEC 112-01-03) character or combination of characters denoting a quantity.
Note : a simple quantity symbol is preferably one, or in some cases two, letters of the Latin or Greek alphabets and may include subscripts, superscripts, or other modifying signs. The letters are in italic (sloping) type, using preferably a font with serifs. The subscripts and superscripts are printed either in roman (upright) type, or, when they denote quantities, variables, or running numbers, in italic (sloping) type. See ISO 80000-1 and IEC 60027-1 for more details and for the combination of symbols. Also known as symbol of a quantity.