90% line in JMeter aggregate report

I considered 90% line is the response data 90% users will see, but recently realized this was wrong. JMeter online Help has detailed explanation about every item in Aggregate report.

The 90% line tells you that 90% of the samples fell at or below that number. However, it is more meaningful than average in terms of SLA. We expect it within 2x of average time. That is, if average time is 500ms, we expect 90% line is less than 1000ms. Otherwise the system fluctuates a lot.