Jet streaks are localized regions of very fast winds embedded within the jet stream. (The jet stream is the fast moving river of air at the level of 250 mb in summer and 300 mb in winter, or approximately 31,00- 34,000 feet.)
The location of the jet streak within the jet stream is important because areas to the right and left sides of the jet streak’s “exit” and “entrance regions” have enhanced upward and downward motions causing clouds and precipitation.
While the area of jet streak has the fastest winds, the jet streak itself moves within the jet stream at a slower speed. More info here.