This indicates that the price range between the open and close of this candle was relatively small, and that there was not a lot of volatility during that time period.
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.