An EMA — short for exponential moving average, though the name really does not matter — is simply a smoothed line drawn through the price to reveal the underlying direction, cutting straight through all the jagged day-to-day noise. The exponential part just means it pays more attention to recent prices than to old ones, so it keeps up with what is happening now.
SeerSignals compares a faster line (which averages roughly the last 20 periods) against a slower one (the last 50). When the fast line sits above the slow line, the trend is genuinely pointing up; when it slips below, the trend is pointing down. It is the steady backbone that tells you which way the wind is really blowing, underneath all the wiggles.