an unofficial but not completely illegal system in which products are bought and sold

The store sells designer clothes and shoes sourced from the grey market. 这家商店出售从灰色市场进货的名牌服装和鞋子。

buying and selling of a company's shares before they are available officially

First dealings in the company's shares will start on the grey market on 27 March and formal trading begins on 2 April. 这家公司的股票将于3月27日开始进入暗盘市场，然后在4月2日正式上市交易。

people over about 50, considered as a group to which products can be sold

Motorbike manufacturers are selling to the grey market as much as to younger people. 摩托车制造商们卖给白发市场的摩托车和卖给年轻人的一样多。