[SOLVED] wrk --latency the mean of latency distribution

i use wrk to test my service

wrk -t2 -c10 -d20s --latency http://192.168.0.105:8102/get

output

  2 threads and 10 connections
  Thread Stats   Avg      Stdev     Max   +/- Stdev
    Latency   525.29ms  210.25ms   1.73s    82.12%
    Req/Sec    11.21      7.05    40.00     65.48%
  Latency Distribution
     50%  489.47ms
     75%  570.62ms
     90%  710.66ms
     99%    1.56s 
  377 requests in 20.08s, 4.54MB read
  Socket errors: connect 0, read 0, write 0, timeout 1
Requests/sec:     18.77
Transfer/sec:    231.74KB

but i do not understand the mean of Latency Distribution

  Latency Distribution
     50%  489.47ms
     75%  570.62ms
     90%  710.66ms
     99%    1.56s