黄牛是指在合法销售途径以外垄断和销售限量参与权与商品以图利的中介人的俗称。黄牛一词来源于20世纪的上海，是指票贩子们联群抢购票时常“有如黄牛群之骚动”，故将他们称为黄牛或黄牛党。因黄牛行为连带匿名炒卖图利的行为严重影响到正当销售途径，故在很多地方皆属违法。

现在引申至所有能获取之特殊方法（或典型的排队，或囤积限量商品，或像「司法黄牛」般靠着特殊的社会地位或利益关系）有规模的垄断图利的商品（不一定是票证，也可以是护照轮候号码、表格、或有收藏价值之物品如签名球衣、限量发行之纪念品等等）或服务，而社会上有殷切需求的民众或愿出高价接受就会有黄牛的出现；就算非为图利而出售，某程度上亦反映着商品流传的渠道与其商业模式的公正性。

Ticket resale (also known as ticket scalping or ticket touting) is the act of reselling tickets for admission to events. Tickets are bought from licensed sellers and are then sold for a price determined by the individual or company in possession of the tickets. Tickets sold through secondary sources may be sold for less or more than their face value depending on demand, which tends to vary as the event date approaches. When the supply of tickets for a given event available through authorized ticket sellers is depleted, the event is considered "sold out", generally increasing the market value for any tickets on offer through secondary sellers. Ticket resale is more common in sporting events and music events/concerts.