int argc (in) Number of elements in argv.
char *argv[] (in) Array of strings containing commandline arguments.
Tcl_Main acts as the main program for most Tcl-based applications. It is not called main because it is part of the Tcl library and having a function main in a library (particularly a shared library) causes problems on many systems. This would also make it hard to use Tcl in C++ programs, since C++ programs must have special C++ main functions.
Normally each application contains a small main function that does nothing but invoke Tcl_Main. Tcl_Main then does all the work of creating and running a tclsh-like application.