Definition

A bruise on the neck (or other exposed skin) caused by aggressive kissing or sucking; a visible badge of makeout honor that you'll inevitably regret by Monday morning.

Example Usage

Dave had such a nasty hickey from the party that he had to wear a turtleneck to work for a week.

Source: Urban Dictionary (https://www.urbandictionary.com/define.php?term=hicky&defid=7770)