System Time is 10 Digit , How?

System Time is 10 Digit , How?

I have question about the current system time, i have software based on
command line. when i run that software , it show me the time at begin of
execution and after execution. Show me the current system time is :
1378258559 then the program executed show me the current system time is
:1378258570 i do not know is the in seconds or minutes. How the 1378258559
is calculated. The different between two numbers id 11 . Is the any answer
from you. FYI, The current time in my system is 9:50 AM. Date is
04/09/2013 thanks