Focus on the pronunciation of set sth (off) against sth
English definition of “set sth (off) against sth”
set sth (off) against sth — Phrasal Verb with set
/set/ verb (setting, set, set)
› TAX to say that an amount of money should be considered a cost of your business and that therefore you should not pay tax on it: You can set off anything you spend on computer equipment against tax.