Do you know CRT?

CRT is NOT Cathode Ray Tube.
As I know, CRT is C RunTime Library's CRT.

And crt0;
in the wikipedia,
crt0 (or crt0.o, gcrt0.o, mcrt0.o) is a set of execution startup routines (usually part of the C standard library), platform-dependent, required in order to compile using the gcc and other GNU tools.
crt stands for 'c runtime'