TFS: Tether Line

Tether line indicator is the first component of TFS trading strategy.
It was named this way because stock prices have a tendency to cluster
around it. It means that stock prices tend to move away from the midpoint
between their 50-day highs and lows, then return to that midpoint at some
time in the future. On a chart, it appears as though the stock price is
tethered to this line, and hence the name.