ما معنى Moving-average crossover, linear filter؟

A moving-average crossover with windows $n < m$ is the logarithm of the ratio of the average of the last $n$ prices to the average of the last $m$ prices; the classic rule is long when it is positive. A linear filter of returns is a predictor of the form $\sum_{j \ge 0} w_jr_{t-j}$ with fixed weights $w_j$.