( Current High of Day + Current Low of Day ) / 2, to get the mid point. It is a useful tool to identify buy side or sell side control, along with vwap.
In true TradingView spirit, the author of this script has published it open-source, so traders can understand and verify it. Cheers to the author! You may use it for free, but reuse of this code in a publication is governed by House Rules. You can favorite it to use it on a chart.