What is the meaning of 'real', 'user' and 'sys' in the output of time command.

Issue

• What is the meaning of real, user and sys in the output of time command.

# time dd if=/dev/sda of=/dev/null bs=1M count=4096 iflag=direct
4096+0 records in
4096+0 records out
4294967296 bytes (4.3 GB) copied, 13.8631 s, 310 MB/s

real    0m13.867s
user    0m0.008s
sys 0m0.330s