__libc_start_main and _start

What is __libc_start_main and _start?Stack Overflow

__libc_start_mainrefspecs.linuxbase.org

The __libc_start_main() function shall perform any necessary initialization of the execution environment, call the main function with appropriate arguments, and handle the return from main(). If the main() function returns, the return value shall be passed to the exit() function.