time_t
From cppreference.com
Defined in header <time.h>


typedef /* unspecified */ time_t; 

Arithmetic type capable of representing times.
Although not defined, this is almost always a integral value holding the number of seconds (not counting leap seconds) since 00:00, Jan 1 1970 UTC, corresponding to POSIX time.
See also
returns the current calendar time of the system as time since epoch (function)  
(C11) 
converts time since epoch to calendar time expressed as local time (function) 
(C11) 
converts time since epoch to calendar time expressed as Coordinated Universal Time (UTC) (function) 
C++ documentation for time_t
