Relative volume compares today's volume to the stock's own average. It's the single most-watched sign a name is in play.
Relative volume (RVOL) is today’s volume divided by the stock’s typical volume for the same time of day. RVOL of 1.0 is an average day; 5.0 means five times the usual participation.
Price moves need fuel. A breakout on average volume often fails because nobody new is participating; the same breakout on high RVOL signals unusual demand. That is why day-traders scan for RVOL before almost anything else — it separates “in play” names from dead ones.
RVOL is descriptive, not predictive: high volume can mark a top just as easily as a launch. Use it as a filter (is this name worth watching?), then let the actual setup and its base rate decide the rest. Also beware low-priced names — huge percentage volume spikes on penny stocks are noisy.