Real Dictionary

hacking jacket
countable noun: A hacking jacket is a jacket made of a woollen cloth called tweed. Hacking jackets are often worn by people who go horse riding.

hacking jacket in American English
a jacket worn by horseback riders, usually with slanting pockets and side or rear vents
noun: a riding jacket having a tight waist, flared skirt, slanted pockets with flaps, and slits or vents at the sides or back

hacking jacket in British English
noun: a riding jacket with side or back vents and slanting pockets