"-iles" terminology for the top half a percent The top 25% is the top quartile.
The top 10% is the top decile.
The top 1% is the top percentile.
Is there an equivalent for the top 0.5%  i.e. 1-in-200?
 A: It's called the top half-percentile or upper half-percentile. Google
"top half-percentile"
or
"upper half-percentile"
to find these terms used in practice, most often in economics.
A: There is percent (%) and permille (‰) so you could say the top five permille.
However, the only occurrences of the latter's use I can find are by one set of authors in two articles at http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4228404/ and https://openi.nlm.nih.gov/detailedresult.php?img=PMC4228404_1476-069X-12-92-1&req=4.
They may be the same occurrences found in 1st percentile, 2nd percentile… But how to say “2.5th” percentile?
A: The general term for these segments is 'quantile', i.e. the top 0.005 quantile is the data segment you are looking for. Quantiles are in a range of [0, 1]. We have separate names for the notable/frequently used quantiles (terciles, quartiles, percentiles, etc.), but we don't have one for the rest. Technically I guess you can come up with a name for them if you know Latin, like 'bicentile' but no one would understand it and you would end up explaining it anyways.
