BTC OTC Discount talk clarifications

[cryptomatch]

Can OTC specialists be kind enough to provide clarity on defining the

Buyer and seller side discount definitions?

i.e. the discounts are usually listed as 5/3 or  gross -4% discount -2%, buyer net discount 3%. I am just try to figure out what

gross and net represent as well where the mandate, middleman commissions fit in?

Appreciate explanation