Stale Lines: a sportsbook moved hard in the last 3 hours, and a pick'em app or a slower book still shows the old number. That old number is the bet, until it moves too.
Steam: two or more books moved the same way within about 45 minutes. Big money or news just hit the line.
Momentum: a line drifting steadily one way over the last 6 hours. Useful for timing: get in early when it is drifting your way.
For player props FanDuel and BetOnline count most, then Pinnacle and DraftKings; for game lines Pinnacle counts most. Signals only start from a sportsbook or prediction market moving (never from a pick'em app); GG.bet's esports prices jump around too much, so they are shown but never set off a signal on their own. Open is the first price we saved for that game. Games drop off the moment they start. Updated about every 10 minutes.