The number of shares transacted every day. Since there is a seller for every buyer, one can think of the trading volume as half of the number of shares transacted. That is, if A sells 100 shares to B, the volume is 100 shares.
TRADING VOLUME
Meaning of TRADING VOLUME in English
Campbell R. Harvey. Hypertextual finance English glossary. Английский словарь гипертекстовых финансов. 2012