Market Indicators
  
You're camping deep in the woods. No phone reception and no data. Yet, you still want to know what the weather will be like today. So you dip into your scout training and look for some weather indicators...things like temperature, dew point, barometric pressure, stampeding deer, etc.
Market indicators work the same way. They allow you to test how the market is performing. Each one provides a part of the picture...taken together, you can often figure out what's on the horizon.
Market indicators include things like the advance-decline line, a measure of how many stocks are moving up versus how many are moving down. Or moving averages. These flatten out day-to-day volatility in a stock's (or index's) performance and shows the longer-term, more stable trend line.