High jinks is a plural noun referring to loud chaotic play, specifically characterized by its high energy and wildness. It can also be spelled hijinks. Some say that high jinks is used within the United States, while hijinks is found outside. However, we found that there is a good mix of either spelled used in all locations. And while the dictionaries list hijinks as the variant spelling, it is growing in popularity as the preferred spelling.
The term seems to come from the verb jink which means to dodge or weave unexpectedly. It can also be used as a noun for a dodge or maneuver. When it is plural, jinks, it takes on a playful meaning like pranking someone. So high jinks is high energy play.