The 52-week high is the highest price a transaction has occurred at in an asset over the last 52-weeks (approximately one year, so it is also called the yearly high).
Further Explanation of the 52-Week High
Whether an asset is trading near, or creating a new, 52-week high gives traders insight into how the stock is performing relative to the last year. An asset that is near the 52-week high is showing strength, as the price is near the highest level it has been all year. A price that continually makes new highs is in an uptrend because the price is continually pushing higher. When the price is not near its 52-week high it means it is weaker than it was at some other point in the year.
Some traders view an asset at a yearly high as a good thing, and try to buy assets which are trading near those highs. An asset needs to rise to reach a 52-week high, so the thinking is that the asset will continue to rise. If you already purchased an asset, that asset trading near its 52-week high, or creating new highs, is a positive sign.
Other traders view a stock that is trading near a 52-week as too high of a price to pay for it, since it could have been purchased at a lower price over the last year. While these traders view the price as too high to get in, if they already bought then seeing the asset move to a new yearly high is a positive sign because they are making money.
The 52-week high is not a definitive signal to trade or not to trade; it is simply the highest price over the last year. How traders interpret it is up to them. The one year time frame is not relevant to all traders. A day trader for example, who places trades that last minutes or even seconds, will gain little insight from knowing the 52-week high. A long-term investor, holding positions for 10 years or more, may also have little interest in the yearly high. They may be more interested in the high price of an asset over the last several years. For traders taking trades that last weeks, months or a couple years, the 52-week high may be relevant as it provides trading opportunities (if the trader has a strategy for trading near yearly highs) over those time frames.
Further Reading On This Topic
The following articles are loosely based on the 52-weeks highs, or provide a greater understanding of how prices move.