Terminology:
fio = https://github.com/axboe/fio/
us = microsecond = (1 / 1 000 000) second
stdev = standard deviation

Quick explanation:
1. Latency:

2. IOps

Detailed information are available in FIO’s How-To (§ 6.0 Interpreting the output)

Example of my configuration (random writes):

[global]
bs=4k
ioengine=libaio
iodepth=4
# was 1g
size=1g
direct=1
runtime=60
# directory=/bcache
directory=/emcpower
filename=ssd.test.file


[rnd-read]
thread=1 # works on threads instead of forking jobs
group_reporting=1 # (group to which it belongs to)
nrfiles=20
name=Random read
rw=randread
# stonewall
numjobs=20

and results:

Random read: (g=0): rw=randread, bs=4K-4K/4K-4K/4K-4K, ioengine=libaio, iodepth=4
...
fio-2.2.10
Starting 20 threads

Random read: (groupid=0, jobs=20): err= 0: pid=20356: Fri Sep 18 14:50:30 2015
  read : io=20480MB, bw=1719.2MB/s, iops=440319, runt= 11907msec
    slat (usec): min=3, max=1424, avg= 8.62, stdev= 4.36
    clat (usec): min=30, max=4547, avg=171.08, stdev=74.76
     lat (usec): min=74, max=4556, avg=179.86, stdev=74.85
    clat percentiles (usec):
     |  1.00th=[   85],  5.00th=[   93], 10.00th=[   99], 20.00th=[  109],
     | 30.00th=[  121], 40.00th=[  137], 50.00th=[  153], 60.00th=[  171],
     | 70.00th=[  193], 80.00th=[  221], 90.00th=[  270], 95.00th=[  314],
     | 99.00th=[  422], 99.50th=[  466], 99.90th=[  572], 99.95th=[  612],
     | 99.99th=[  740]
    bw (KB  /s): min=85432, max=89608, per=5.01%, avg=88263.86, stdev=448.71
    lat (usec) : 50=0.01%, 100=10.26%, 250=76.45%, 500=12.99%, 750=0.28%
    lat (usec) : 1000=0.01%
    lat (msec) : 2=0.01%, 4=0.01%, 10=0.01%
  cpu          : usr=5.98%, sys=25.04%, ctx=3909260, majf=0, minf=1604
  IO depths    : 1=0.1%, 2=0.1%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, >=64=0.0%
     submit    : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
     complete  : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
     issued    : total=r=5242880/w=0/d=0, short=r=0/w=0/d=0, drop=r=0/w=0/d=0
     latency   : target=0, window=0, percentile=100.00%, depth=4

Run status group 0 (all jobs):
   READ: io=20480MB, aggrb=1719.2MB/s, minb=1719.2MB/s, maxb=1719.2MB/s, mint=11907msec, maxt=11907msec

Disk stats (read/write):
    dm-7: ios=5146410/0, merge=0/0, ticks=872432/0, in_queue=906207, util=100.00%, aggrios=5242880/0, aggrmerge=0/0, aggrticks=884520/0, aggrin_queue=0, aggrutil=0.00%
    bcache0: ios=5242880/0, merge=0/0, ticks=884520/0, in_queue=0, util=0.00%, aggrios=2641920/6, aggrmerge=0/5, aggrticks=0/0, aggrin_queue=0, aggrutil=0.01%
    md0: ios=5283840/0, merge=0/0, ticks=0/0, in_queue=0, util=0.00%, aggrios=2641920/0, aggrmerge=0/0, aggrticks=433228/0, aggrin_queue=439215, aggrutil=100.00%
  nvme0n1: ios=2650725/0, merge=0/0, ticks=436106/0, in_queue=442247, util=99.96%
  nvme1n1: ios=2633115/0, merge=0/0, ticks=430351/0, in_queue=436183, util=100.00%
  emcpowera: ios=0/13, merge=0/10, ticks=0/1, in_queue=1, util=0.01%