- Total is the total number of people with that surname.
- Rank is the position in the list of names ordered by total (eg, a rank of 1 means that it's the most common name, and a rank of 10 means it's the tenth most common, etc).
- Frequency is the percentage of people with that surname.
- Per million people is the number of people with that surname per million of the population.
All of these are approximate figures, and the current figures especially so. The 1881 census figures are correct for what was recorded on the census, but we don't really know how accurate it was. At least, though the 1881 figures won't change, as it's a snapshot of a point in time. The current figures, by contrast, are variable according to births, deaths, migration and marriages, so the values shown here are only a best approximation to whatever was the case when the underlying data was collated and will not be the same as whatever the values are right now.
'N/A' indicates that we don't have data for this name in that country or time (usually because it's quite uncommon there and our stats don't go down that far). It doesn't mean that there's no-one there with that name at all!
For less common surnames, the figures get progressively less reliable the fewer holders of that name there are. This data is aggregated from several public lists, and some stats are interpolated from known values. The margin of error is well over 100% at the rarest end of the table!
It's possible for a surname to gain in rank and/or total while being less common per million people (or vice versa) as there are now more surnames in the UK as a result of immigration. In mathematical terms, the tail has got longer, with a far larger number of less common surnames.