There are many ways to report on gender pay gaps, for example averages can be calculated as a mean or median, and the figures can be based on basic (hourly or annual) pay or (include) bonus pay.

The UK Equality Act requires disclosure on a range of variables, and in relation to those disclosures this metric equates to the mean hourly wage difference. Check whether the company disclosed to the UK Equality Act and find their reports here: https://gender-pay-gap.service.gov.uk/Viewing/search-results

For companies that are not bound by the UK's equality act, it can be quite rare to find any figures about gender pay gaps at all, and so this metric is designed to be quite flexible. Ideally, the answer would cover all of the companies employees globally, but this information is rarely provided at the scale of global operations. 

If only one figure is reported, use that figure and make a comment explaining how it was calculated if that information is provided. In particular, does it cover employees globally or just in a particular country? Is it a mean or a median, or do they state this? Does it include bonus pay or is it based on a basic hourly rate? Comments that record these details are important because they help us to figure out how companies are reporting, and therefore how their answers should be interpreted.

Sometimes this data is expressed as a ratio, for example, 0.87 to 1 - this would be recorded as 87%.

Numbers greater than 100% are acceptable, these would indicate that female workers at  the company earn more than male workers on average.