I'm really not sure what _far does, but from the context I'd say it's some preprocessor definition somewhere in the source code.
As for the rest constchar cmd_cls_scr[] = {27,'[','2','J',0};, this creates a constant character array called cmd_cls_src and assigns it the 5 characters you see there (note: 27 will be whatever ASCII value 27 is, and 0 is the null terminating character you find at the end of c-strings i.e. '\0')