This is the total number of keywords that your target website, subsection, or URL ranks for in the top 100 organic search results in Google, across all the countries in the Ahrefs database.
It's calculated by checking the ~500 million keywords in our database and counting how many times your target ranks in the top 100 search results. Note that when your target ranks for a keyword more than once, it’s counted multiple times.
Remember that it will almost always be smaller than the actual number of keywords you're ranking for, because certain unique search queries may not be in our database. With that said, Ahrefs updates its keyword database with newly-discovered search queries every month. We also regularly purge search queries from our database if their popularity fades.
One final thing to note about our organic keywords metric is that it’s often country-specific.
Take our Top pages report for example:
The number of keywords shown here is for the United States only.
If you'd like to see this data for all countries, select that option from the drop-down menu.