What Is Break of Structure (BOS) in Trading?

Break of structure, usually written BOS, is trader shorthand for price closing beyond the last significant high or low on a chart. Nothing more complicated than that. A bullish break of structure is a close above the previous peak; a bearish one is a close below the previous trough. It confirms that the trend already running is still running.

Why does it get its own acronym?

Because it comes from smart money concepts, a style of chart reading that describes what price did rather than what an indicator says about it. In that language the chart is a structure made of highs and lows, and the structure breaks every time price steps past the last one. Picture a staircase. Each step up is a bullish break of structure, and as long as the steps keep rising you are still on an upward staircase.

The mistake nearly everyone makes

Treating a break of structure as a buy or sell signal. It is a description of something that has already happened, which is why a Bitcoin chart can print a dozen of them in a week and still finish lower than it started. Two habits help. Wait for a candle to close beyond the level instead of reacting to a wick that pokes through and retreats. And check the structure on a higher timeframe before acting on a small one, because a bullish break on a five-minute Ethereum chart inside a falling daily trend is a very different trade from the same break on the daily itself.

Open any chart, mark the last three breaks of structure you can find, and ask of each one whether the higher timeframe agreed. That single question filters out most of the bad ones for free. From here, market structure itself is the foundation worth reading first, and the market structure shift is the break that points the other way.