Secondly,the trade amount of business to custom...

Secondly,the trade amount of business to custom...
Secondly,the trade amount of business to custom(B2C) and custom to custom(C2C) accounts for the most part of the total trade amount of e-shopping.请帮忙翻译.尤其是(B2C)和(C2C) 是什么,没见过此种表达.