IV is not directional — a high-IV environment does not predict whether the stock goes up or down, only how much it moves. That is why straddles and strangles profit from a big move in either direction. It is also why selling premium when IV is high and buying premium when IV is low is the universal premium-trader's edge: you are buying low and selling high at the volatility level, regardless of stock direction.
IV is reported as a percentage. SPY at 12% IV is dramatically different from a meme stock at 200% IV. To compare across stocks, traders use IV rank or IV percentile — which place the current IV relative to its 52-week range. An IV rank of 80 means current IV is in the top 20% of the past year. That single number is more actionable than the raw IV value.