C Programming/C Reference/time.h/ctime
In computing, ctime is the number of seconds since 0:00:00 January 1, 1970 UTC. Commonly stored as a 32 bit signed integer, this number is used for pinpointing dates in many computers and operating systems, such as Linux and UNIX variants, as well as some programming languages. It will overflow in 2038 and cause the year 2038 problem; some expect this will be a profitable non-event similar to Y2K.
ctime is also a Unix library call which returns the local time as a human readable ASCII string.
ctime in a Unix filesystem is a file attribute which tells when the file's inode was last modified.