Trix (or TRIX) is a technical analysis oscillator developed in the 1980s by Jack Hutson, editor of Technical Analysis of Stocks and Commodities magazine.
It shows the slope (i.e. derivative) of a triple-smoothed exponential moving average.
TRIX is a triple smoothed exponential moving average used in technical analysis to follow trends.
TRIX crossing above its signal line implies that the price will likely move higher.
TRIX crossing below its signal line implies that the price will likely move lower.
[1] Trix is calculated with a given N-day period as follows: Like any moving average, the triple EMA is just a smoothing of price data and, therefore, is trend-following.
A rising or falling line is an uptrend or downtrend and Trix shows the slope of that line, so it's positive for a steady uptrend, negative for a downtrend, and a crossing through zero is a trend-change, i.e. a peak or trough in the underlying average.