A Swing High is a peak in price movement for an asset.
A swing high can occur on any trading time frame. Swing highs are based on the number of data points in a series. So, if you are looking back over the past 3 bars, you will want to find the highest price peak in the chart pattern for that series. In order to find important price swings, you will want the look back series to be on the order of 10-20 bars. Swing highs can be used to find critical price junctures and are often an acceleration point for price movement.
A swing high is also a good place to enter stop loss orders for short positions.