The highest and lowest price a stock has traded at over the trailing 12 months.
A stock hitting a new 52-week high means it's trading above every closing price from the past year — often read as a sign of strong momentum or improving fundamentals, though it can also signal a stock has run ahead of its valuation. A new 52-week low is the inverse, and can reflect either a genuine deterioration in the business or a temporary, overdone sell-off.
Neither on its own is a buy or sell signal — the more useful question is always why the stock is at that level.