Signals are called by various names—signals, indicators, predictors, calculators, features, alpha, and so on—but they all have roughly the same meaning. (Location 701)
A trading signal is a well-defined piece of intelligence that is derived from incoming market data information, limit order books or trade information that allows a trading strategy to get a statistical edge (advantage) vis-à-vis other market participants and, thus, increased profitability. (Location 702)
Often, a lot of algorithmic trading systems combine a lot of different kinds of signals in order to gain a bigger edge than individual signals provide. The approach is to essentially combine different signals that have different predictive abilities/advantages under different market conditions. (Location 708)
the trend strategy uses speed, whereas the momentum strategy uses acceleration. (Location 974)