IV Rank, also referred to as the Implied Volatility Rank or IVR, is a measurement of how the current IV level of a given equity compares to the last 52 weeks of historical data. 

The IV Rank value is provided on a scale between 0 - 100, where a value of 0 would represent the lowest IV value of the year whereas a value of 100 would represent the highest IV value in the previous 52 week period.

For example:
In the last 52 week period ticker ABC's IV ranged from 40% to 80%. 

If ticker ABC's IV is currently at 60% it would be an IVR of 50. 

IV Rank Resources:
IV Rank for all optionable equities can be found on the Ticker Screener