Used in the context of general equities. Having either buy or sell interest at the indicated price level and side of a preceding trade . "Open on the buy/sell side," means open to customer buyers/sellers, not that he/she wants to buy/sell but rather that he wants to find buyers/sellers (meaning that he/she is a seller/buyer). Antithesis of clean .
OPEN
Meaning of OPEN in English
Campbell R. Harvey. Hypertextual finance English glossary. Английский словарь гипертекстовых финансов. 2012