A 52-week high is the highest price that a stock has traded at in the last year. 
Many investors use 52-week highs and 52-week lows as a factor in determining a stock's current value and as a predictor of future price movements. As a stock trades within its 52-week price range (the range that exists between the 52-week low and the 52-week high), investors may show increased interest as price nears either the high or the low.