I can take that one (I wonder if this will be a crosspost with someone else) EDIT: Yes it was! ;-)
If you take a set of numbers and sort them into increasing order, the middle value is the "median" value.
The median is important because 50% of the numbers will be less than (or equal to) the median and 50% will be greater than (or equal) to the median.
So the median value represents a middle-ground value.
If we now slide along and look at the larger numbers in that list, we can reach a value that has 95% of the (lower) values to the left of it and 5% of the (higher) values to the right of it.
That's the 95% value that you often hear about.
If we slide even further to the right in our fictional list of numbers, we reach a value where 99% of the values are to the left and only 1% are to the right.
That would be the 99% value you sometimes hear about.
The 99% value is handy because sometimes we may get the occasional rogue values that are too big to be true and are probably errors in the readings.
If we were to look at the maximum value, the maximum would contain these rogue values and give a misleading impression of values being huge.
By only looking at the 99% value (instead of the maximum value) we get a better feel for the "meaningful maximum" that ignores those rogue values in the top 1%
The 95% value is handy for similar reasons. It ignores the top 5% and is another convenient way of getting a feel for the "meaningful maximum" by ignoring erroneous large spikes that are probably just noise and not trustworthy.
Does that help?
EDIT2: I could get pedantic and start talking about the terms "less than", "less than or equal to", "greater than" & "greater than or equal to" but that would not help to convey the general feel for the terms: median, 95%, 99% and maximum.
EDIT3: The current version of
OSCAR sometimes claims that a value is the "maximum" value when it is actually a "99%" or maybe a "95%" value.
The upcoming release of
OSCAR is changing so that the terms are used consistently and correctly. I believe it's fixing a legacy thing from the Sleepyhead days.